Violent clashes broke out in numerous centres, including the big cities of Alexandria and Suez.
Protesters managed to force the retreat of police in some major streets in Suez, attacking officers and security vehicles.
Tanks arrived on the streets, some guarding the remains of a police station that had been set alight earlier.
Dozens of protesters climbed onto some of the tanks, and unconfirmed reports say shots were fired.
Some latest reports say some 400 people have been wounded in Cairo alone.
The government reports widespread looting and ransacking of government buildings.
The headquarters of the ruling party was also set on fire and the army has set up barricades around parliament.