Thousands of Egyptians have taken to the streets to demand an end to President Hosni Mubarak's 30-year rule.
Three people have been killed in the unprecedented countrywide protests inspired by the revolt that brought down Tunisia's president.
However, two protesters in the city of Suez, east of Cairo, died as a result of rubber bullets, security and medical sources have said.
State television said a security officer died in central Cairo after a blow to the head from a missile.
Some protesters were beaten hard by police with sticks. Others, in a rare show of nerve against a huge national security operation, chased police down side streets.
Sites such as Facebook and Twitter have been key tools for activists in galvanising protesters. Harvard University's Herdict web monitoring service reported that Egyptians said the Twitter website was blocked on all Internet Service Providers.
Egyptians have the same complaints that drove Tunisians onto the streets: surging food prices, poverty, unemployment and authoritarian rule that smothers public protests quickly and often brutally.