The state news agency MENA said Mubarak was "clinically dead" when he arrived at the hospital and that doctors used a defibrillator on him several times. It initially said the efforts were not successful.
But the official said Mubarak was put on life support. He had no further details on his condition. The official spoke on condition of anonymity because he was not authorized to talk to the press.
The developments add further layers to what is threatening to become a new chapter of unrest and political power struggles in Egypt, 16 months after Mubarak was ousted by a popular uprising demanding democracy. Egyptians were uncertain about Mubarak's fate, about who will succeed him and about whether his successor will have any power.
The campaign of Mubarak's former prime minister, Ahmed Shafiq, said Tuesday he has won Egypt's presidential election, countering the Muslim Brotherhood's claim of victory for its candidate, Mohammed Morsi.
The election commission is to announce the official final results on Thursday and no matter who it names as victor, his rival is likely to reject the result as a fraud. If Shafiq is declared winner in particular, it could spark an explosive backlash from the Brotherhood.
The Brotherhood, Egypt's most powerful political group, is already escalating its challenge against the ruling military over the generals' move this week to give themselves overwhelming authority over the next president. Some 50,000 protesters, mostly Islamists, massed in Cairo's Tahrir Square on Tuesday evening chanting slogans in support of Morsi and denouncing the generals' power grab.
The health crisis of Mubarak, who is serving a life prison sentence, is yet one more thing to stoke the heat.
Moving Mubarak out of prison is likely to further infuriate many in the public. Many Egyptians have been skeptical of earlier reports that his health was worsening since he was put in prison on June 2, believing the reports were just a pretext to move him to another facility. There is a widespread suspicion that security and military officials sympathetic to their old boss are giving him preferential treatment.
Details of the crisis were still sketchy. Earlier the news agency and officials said that while at the Torah Prison hospital he suffered a "fast deterioration of his health." His heart stopped beating until he was revived by defibrillation, then he suffered a stroke.
At that point, he was moved from the prison hospital to Maadi military hospital - notably the same one where his predecessor Anwar Sadat was declared dead more than 30 years ago after being gunned down by Islamic militants. That was when MENA reported him "clinically dead."
The criteria for using that term are "poorly defined," said said Dr. Lance Becker, a University of Pennsylvania emergency medicine specialist and an American Heart Association spokesman. "In its crudest form, clinical death just means that a doctor thinks he's dead - somebody standing at the bedside believes he is dead," he said.
"My speculation would be that he had that sort of event where his heart temporarily stopped," said Becker, who is not involved in Mubarak's treatment. "That doesn't mean that it's irreversible," and life support can be used to keep his blood circulating and replace breathing if he is unable to do so on his own, Becker said.
Mubarak's condition brought to mind former Israeli Prime Minister Ariel Sharon - though it was not known if there was any medical similarity in their conditions. Sharon suffered a massive stroke on 2006. Intensive treatment and repeated operations by a team of brain surgeons stabilized his condition, but he never regained consciousness. Sharon, 84, is still alive but remains on life support in a deep coma.
Mubarak has been serving a life sentence at Cairo's Torah Prison for failing to stop the killing of protesters during the 18-day uprising against his rule last year. The verdict against him has already been a spark for protests - thousands massed in Tahrir when the court acquitted him and his sons on separate corruption charges and cleared several top security chiefs on the protester killings.
The multiple disputes have turned a moment that was once anticipated by some as a landmark in Egypt's post-Mubarak transition - the election of the first civilian president in 60 years - into a potentially destabilizing snarl.
Shafiq's campaign spokesman, Ahmed Sarhan, told a televised news conference that Shafiq won 51.5 percent of the vote and that the claim of victory by Morsi was "false."
"Gen. Ahmed Shafiq is the next president of Egypt," said Sarhan. He said Shafiq won some 500,000 votes more than Morsi, of the fundamentalist Brotherhood.
The Shafiq campaign's claim came just hours after Morsi's campaign repeated their claims of victory, saying Morsi had won 52 percent of the vote compared to Shafiq's 48.
The Brotherhood first announced Morsi's victory early Monday, around six hours after polls closed. It said its claim was based on returns announced by election officials from each counting center around the country. Each campaign has representatives at every center, who compile the individual returns. The Brotherhood's compilation during the first round of voting last month proved generally accurate and, when it announced its victory early on in that race, it raised no objections.
But this time, Shafiq's campaign countered quickly, saying early Monday that its ongoing count showed their man ahead. Tuesday's announcement was its first claim that it had won.
Shafiq, a former air force commander who was named prime minister during Mubarak's last days, is seen by his opponents as likely to preserve the military-backed police state that his former boss headed for three decades. He, in turn, has presented himself as a strongman able to keep Egypt stable and out of the hands of the Brotherhood, playing on fears the group will turn the country into an Islamic state.
Just as polls closed on Sunday night, the military - which has ruled since Mubarak fell on Feb. 11, 2011 - issued a constitutional declaration that gave themselves power that all but subordinates the new president, a move critics called a "coup" intended to maintain their control over the state even after they nominally transfer authorities to the president by July 1.
The declaration gave the generals legislative powers and control over the process of drafting a new constitution and the national budget. It also shields the military against any kind of civilian oversight and allows the generals to run their own affairs without interference from civilian authorities.
A court ruling also dissolved the Islamist-dominated parliament last week, a verdict that has been endorsed by a decree issued by military ruler Field Marshal Hussein Tantawi. The Brotherhood and its Islamist allies dismissed the decree, arguing that Tantawi had no right to issue it with less than two weeks before the scheduled transfer of power to civilians. Also last week, the military-backed government granted military police and intelligence agents the right to arrest civilians for a host of suspected crimes, a move that many viewed as tantamount to a declaration of martial law.
Thousands were demonstrating in Cairo and the Mediterranean port city of Alexandria Tuesday evening to denounce the constitutional declaration, which also strips the next president of significant powers and the court ruling.
The estimated 50,000 protesters in Cairo's Tahrir Square, birthplace of last year's anti-Mubarak uprising, were mostly Brotherhood supporters and other Islamists joined by a small group of leftist and liberal activists.
"It is not possible to have a revolution and then have military rule and a president with no authority," said protester Mohammed Abdel-Hameed, a 48-year-old schoolmaster who said he came with his son and others to Tahrir from Fayyoum, an oasis province 60 miles (100 kilometers) southwest of Cairo.
"How can they dissolve parliament and spend all that money again on another election? This is a waste of public funds," he said. "If they want blood we are ready to offer blood. I am. So that my son can live free," warned Abdel-Hameed, who wore traditional galabeya robes.
Some protesters gathered outside parliament earlier Tuesday, and a number of lawmakers tried to enter the building but were turned away by security forces. Hundreds of black-clad policemen armed with clubs and shields ringed the building, standing behind metal barricades.
"Wake up, field marshal. We defended our revolution through the ballot boxes," protesters chanted, referring to Tantawi, Mubarak's defense minister for 20 years. "You coward Field Marshal, free parliament," they screamed.
"No revolution that is protected by God will fail," said Saber Ibrahim, a 36-year-old school teacher who came from his native Beni Suef south of Cairo to participate in the rally. "We, the people, gave them (the military) legitimacy and we now are taking back."
On Tuesday former U.S. President Jimmy Carter expressed his concerns. His Carter Center monitored the weekend runoff as it has every nationwide vote in Egypt since Mubarak's ouster in a popular uprising engineered by pro-democracy youth groups.
"I am deeply troubled by the undemocratic turn that Egypt's transition has taken," Carter said in a statement Tuesday. He pointed to the dissolution of parliament and the elements of martial law and said the constitutional declaration "violated the military's commitment to make a full transfer of power to an elected civilian government.
"An unelected military body should not interfere in the constitution drafting process," said Carter, alluding to the military's control over the writing of the charter. Carter is a regular visitor of Egypt, where he often meets with the ruling generals and government leaders.
Amnesty International said the powers acquired by the military could lead to further human rights violations and, unless modified, they would allow the generals "to continue to trample on human rights with impunity."
It said the control of the military over the panel tasked with drafting the constitution allows it to reject any attempt to restrain the military, put it under civilian oversight or hold it accountable for human rights abuses.
Hoda Mahmoud, a 32-year old human resources manager, was out protesting at Tahrir Square on Tuesday. A member of a youth group known as the Revolutionary Socialists, she said her real fight is with the military and predicted that the Brotherhood may eventually back down.
"The fight is in the street, not one about political settlements," she said, alluding to the Brotherhood's reputation for political opportunism and appetite for back-room deals.
Chief Medical Writer Marilynn Marchione in Milwaukee, Wis., contributed to this report