The crowd appeared to include a heavy contingent from the Muslim Brotherhood. Safaa Abu Bakr, 40 years old, a school teacher veiled in gray, said, “State media is part of the regime that we want to topple.”

Protesters there were skeptical the army could guarantee the transition to democracy outlined by Mr. Mubarak. “I have faith that the army won’t open fire at the protesters, but I do not trust the minister of defence,” said Bahaa al-Madani, 32, a lawyer, outside the razor wire that surrounded the building. “I do not trust the ability of the current army leadership to guarantee Mubarak’s promises.”

The crowd outside the heavily guarded presidential palace in the neighborhood of Heliopolis grew quickly, from hundreds midday to thousands later in the afternoon. It wasn’t clear whether Mr. Mubarak was in the palace; several reports said he had left Cairo, possibly for the Red Sea resort of Sharm-el-Sheikh.