This outpouring of people makes it clear that the movement to oust Mubarak, far from losing steam, is only growing stronger and stronger. Of course it's impossible for millions of people to demonstrate day after day, so a strategy is emerging to keep a continuous presence in Tahrir Square at all times, and to bring massive demonstrations at regular intervals. The next natural time for another such demonstration will be after Friday prayers.
Packed shoulder to shoulder in and around the famed Tahrir Square, the mass of people on Tuesday held aloft posters denouncing the president, and chanted slogans "Go Mubarak Go" and "Leave! Leave! Leave!"
Similar massive demonstrations calling on Mubarak to step down are also being witnessed across other cities, including Sinai, Alexandria, Suez, Mansoura, Damnhour, Arish, Tanta, el-Mahalla and el-Kubra.
Tens of thousands were reportedly marching in Alexandria while the number of those protesting in Sinai was estimated to be around 250,000.
Tuesday's protests were by far the biggest since street demonstrations broke out against Mubarak's rule last week.
"The crowd is very diverse - young, old, religious, men, women - and growing by the minute," Al Jazeera's online producer said from Tahrir Square.
"They're chanting the same slogans they've been chanting all week. Someone actually hung an effigy of Mubarak from a streetlight."
Organisers had called for a march by a million people on the day, but the turnout surpassed all expectations.
Soldiers deployed at the square did nothing to stop the crowds from entering.
They have formed a human chain around protesters, and are checking people for weapons as they enter. Tanks have been positioned near the square, and officers have been checking identity papers.
According to reports, the military police have placed barbed wire around Mubarak's residence in Masr el-Gedidah, a suburb east of Cairo.