Egypt's military deployed on the streets of Cairo to enforce a nighttime curfew as the sun set Friday on a day of rioting and chaos that amounted to the biggest challenge ever to authoritarian President Hosni Mubarak's 30-year regime.

Flames rose up across a number of cities from burning tires and police cars. Even the ruling party headquarters in Cairo was ablaze in the outpouring of rage, bitterness and utter frustration with a regime seen as corrupt, heavy-handed and neglectful of grinding poverty that afflicts nearly half of the 80 million Egyptians.

"I can't believe our own police, our own government would keep beating up on us like this," said Cairo protester Ahmad Salah, 26. "I've been here for hours and gassed and keep going forward, and they keep gassing us, and I will keep going forward. This is a cowardly government and it has to fall. We're going to make sure of it."

After nightfall, some of the protesters defied the curfew and were praying on the streets of Cairo.

In one of many astonishing scenes Friday, thousands of anti-government protesters wielding rocks, glass and sticks chased hundreds of riot police away from the main square in downtown Cairo and several of the policemen stripped off their uniforms and badges and joined the demonstrators.

An Associated Press reporter saw the protesters cheering the police who joined them and hoisting them on their shoulders in one of the many dramatic and chaotic scenes across Egypt on Friday.

After chasing the police, thousands of protesters were able to flood into the huge Tahrir Square downtown after being kept out most of the day by a very heavy police presence. Few police could be seen around the square after the confrontation.