Some media reports say he is clinically dead, with Nile TV saying attempts are continuing to revive him.
The 84-year-old is said to have had a stroke, and was moved from prison to life support in an army hospital.
Mubarak was removed in last year’s uprising, and jailed for life earlier this month for his role in the death of protesters before his removal.
There have been frequent reports since then that his health has deteriorated, many of which have proved wrong.
The news comes as tens of thousands of people protest in Cairo’s Tahrir Square against a move by the ruling military council to assume new powers.