Overnight, state media reported that the 84-year old former president, who was ousted in last year's uprising, suffered a stroke and was put on life support.
He was later transferred to a military hospital from the Cairo prison hospital where he recently began serving a life sentence.
The security officials said Wednesday that a team of 15 doctors was supervising the condition of Mubarak, who needed help with his breathing.
The officials spoke on condition of anonymity because they were not authorised to speak to the media.
State news agency MENA and security officials had earlier said that Mubarak's heart had stopped beating.
He had been revived by defibrillation but then had a stroke and was moved from Torah Prison to Maadi military hospital in Cairo.
Early on Wednesday, a small group of Mubarak supporters gathered outside the hospital to pray for his health.
“We are praying for him if he is still alive and if he is dead we will pray for him for God's mercy. We still remember the good things that he has done beside the bad things,” said Mahmoud Abdellah, one of Mubarak's supporters.
Major General Mohsen el-Fangari, a member of the ruling military council, told the Al-Shorouk newspaper website that Mubarak was in a “very critical condition,” but denied he was dead.
The developments came amid threats of new unrest and political power struggles, 16 months after Mubarak was ousted by a popular uprising demanding democracy.
Earlier on Tuesday, both candidates in last weekend's presidential election claimed victory.
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.
Hundreds of Shafiq's supporters took to the streets in Cairo in celebration.
Meanwhile, the Muslim Brotherhood, emboldened by its claim that its candidate won the election, sent tens of thousands of supporters into the street in an escalation of its confrontation against the ruling generals who invoked sweeping powers this week that give them dominance over the next president.
Some 50-thousand protesters, mostly Islamists, protested in Cairo's Tahrir Square, chanting slogans in support of Morsi and denouncing the generals.
The election commission is to announce the official final results on Thursday, and either way the loser is likely to reject the result.
The conflicting claims over the election could further stoke the heat.
If Shafiq wins, it could spark an explosive backlash from the Brotherhood, which has said Shafiq could only win by fraud.
Some Egyptians feel, however, that the military council will not allow any new president to take decisions.
“In my view, the military rules Egypt. To me there is no difference between Morsi and Shafiq, they (Military council) have taken all the power from the coming president. They are the ones who rule Egypt,” said Cairo resident Taha Ahmed.
The sudden health crisis of Mubarak, who is serving a life prison sentence, briefly overshadowed the political standoff.
Moving Mubarak out of prison to Maadi military hospital is likely to further infuriate many in the public.
Many Egyptians have been sceptical 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.
Just as polls closed on Sunday night, the military - which has ruled since Mubarak fell on Feb. 11, 2011 - issued a constitutional declaration giving themselves power that all but subordinates the new president.
Critics called it 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.
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.