Egypt's state news agency has reported that former President Hosni Mubarak is in a coma and has been removed from life support.
The news comes amid huge protests in Cairo's Tahrir Square over last week's presidential election results.
The official announcement said 84-year-old Mubarak's heart stopped beating last night and had to be revived. Afterwards, he suffered a brain stroke and his condition was described as a "fast deterioration of his health."
Doctors then moved the former president from prison to a military hospital in Cairo. The news agency originally said Mubarak was "clinically dead" and put him on life support.
Mubarak had begun serving a life sentence after a court convicted him of complicity in the deaths of protestors in last year's uprisings.
The news comes at a key political moment for Egypt as its people wait for Thursday when results of the presidential campaign will be announced.
Both Mohammed Morsi, the Muslim Brotherhood candidate, and Ahmed Shafiq, a former prime minister, are claiming victory.
The Muslim Brotherhood sent tens of thousands of its supporters to Cairo's Tahrir Square to celebrate and protest recent decisions by the army, which dissolved the parliament and assumed sweeping new powers.