CAIRO — Tens of thousands of anti-government protesters today poured into the streets of Egypt, stoning and confronting police who fired back with rubber bullets and tear gas in the most violent and chaotic scenes yet in the challenge to President Hosni Mubarak’s 30-year rule.

One protester was killed and even a Nobel Peace laureate was placed under house arrest after joining demonstrations.

Groups of thousands of protesters, some chanting “out, out, out,” defied a ban on any gatherings and turned out at different venues across Cairo, a city of about 18 million people, some marching toward major squares and across scenic Nile bridges. Burning tires sent up plumes of black smoke across the city. Security officials said there were protests in at least 11 of the country’s 28 provinces.

It was a major escalation in the movement that began on Tuesday to demand 82-year-old Mubarak’s ouster and vent rage at years of government neglect of rampant poverty, unemployment and rising food prices. Security officials said protesters ransacked the headquarters of Mubarak’s ruling party in the cities of Mansoura north of Cairo and Suez.

Some of the most serious violence today was in Suez, where protesters seized weapons stored in a police station and asked the policemen inside to leave the building before they burned it down. They also set ablaze about 20 police trucks.