There are reports that the headquarters of the ruling National Democratic Party have been set on fire in Cairo as protestors stay out on the streets despite a curfew.
Witnesses have reported tanks on the streets of the capital as the military have been deployed to help the police deal with the protestors.
There have been gunshots and loud explosions on the streets of Cairo outside government buildings.
Tens of thousands of people have been clashing with police calling for an end to President Hosni Mubarak’s 30-year rule.
At least one demonstrator has been killed, while pro-reform leader and Nobel Peace Prize winner Mohamed ElBaradei was placed under house arrest after returning to Egypt to join the dissidents.
Tonight Egyptian state TV announced a 6pm to 7am curfew in Cairo and two other cities.
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 tyres sent up plumes of black smoke across the city as the sun set. Security officials said there were protests in at least 11 of the country’s 28 provinces.
Internet and mobile phone services were largely cut off in an apparent bid to hinder the protest organisers.
The problems have been increasing since Tuesday, when demonstrations began calling for the removal of 82-year-old Mr Mubarak amid rampant poverty, unemployment and rising food prices.
Security officials said protesters ransacked the headquarters of the ruling party in the cities of Mansoura north of Cairo and Suez, east of the capital.
Some of the most serious violence 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 parked nearby.
Demonstrators exchanged fire with policemen trying to stop them from storming another police station and one protester was killed in the gun battle.
The death brought the toll of those killed in four days of protests to eight.
Internet and cell phone services, at least in Cairo, appeared to be largely cut off since overnight in the most extreme measure so far to try to hamper protesters form organising.
However, that did not prevent tens of thousands from flooding the streets, emboldened by the recent uprising in Tunisia.
Meanwhile, dozens of protesters gathered outside the Egyptian embassy in London in a show of solidarity.
The campaigners, many of them expatriates living in London, stood outside the embassy in Mayfair and chanted “down with Mubarak”.
Standing in a cordon on the street, the crowd held banners and flew the Egyptian flag.
Hisham Youssef, who lived in Cairo until two months ago, said the group wanted to speak out on behalf of their countrymen and women.
He said they were calling for Egypt’s president Hosni Mubarak to quit.
“It is time for Mubarak to go,” said Mr Youssef.
“Thirty years of corruption. It used to be a different country. There is no freedom of speech.
“The system has to change, it is time for him to go.
“We are here to show solidarity with the people in Egypt.”