Some of the demonstrators had slept in tents or out in the open overnight in the iconic square, epicentre of an anti-regime revolt that ousted the veteran leader in 2011 after three decades of autocratic rule.
“We intend to stay today and possibly tomorrow. We expect a lot more people to come during the day,” said Omar Abdelkader, a young protester in Tahrir Square.
Around 20,000 people had taken to Tahrir on Saturday after a judge sentenced Mubarak, 84, and his interior minister Habib al-Adly to life for their role in the deaths of more than 800 protesters during last year’s revolt, but acquitted six security chiefs on the same charges.
A senior member of Mubarak’s defence team told AFP the former president would appeal.
Mubarak, the only autocrat toppled in the Arab Spring to be put on trial in person, could have been sent to the gallows as demanded by the prosecution.
Both the toppled dictator’s defence team and lawyers representing his victims said the verdict could easily be appealed.
The verdict prompted outrage inside and outside the courtroom, with protesters staging rallies in Cairo, Alexandria and other Egyptian cities.