It all started peacefully. From 2pm and various points across Cairo, straggling lines of marchers up to a kilometre long snaked their way through the bustling city to the centre. Onlookers clapped from balconies while passengers leaned out of car windows to take photos.

Bashar Abdelmenem, a 22-year-old medical student, said: "I am here because of the poverty and because of the corruption. Nothing in Egypt is going as it should. This is the first chance the people have got to express how messed-up the country is. We want four things. We want the Minister of the Interior to be fired. We want people who have graduated to get jobs. We want the President to limit the time he is in power and we want an end to the emergency law."

Such demands, and even yesterday's initially peaceful protest, would have been unheard in Egypt two weeks ago, before riots against the administration of President Zine al-Abidine Ben Ali in Tunisia suddenly led to the overthrowing of the regime.

Screaming out chants like "No to torture! No to corruption!" and "Egyptians say 'Leave, Mubarak!'" some protesters even applauded the restraint of riot police who had been dispatched around the capital to control the demonstrations. Mariam Tarek, a 20-year-old English student, said: "This is our opportunity to get up and tell the government that we don't want them. More than 50 per cent of the population is below the poverty line. The people need to speak."

But by around 3.30pm, as thousands of people began to converge in downtown Cairo's Tahrir Square, relations between demonstrators and riot police began to turn ugly, protesters screaming: "Allahu Akbar!" fought running battles with police, ripping up paving stones and hurling them at the officers. The security forces responded with tear gas and threw back the rocks hurled by activists.

Saeed Khalil, a 54-year-old engineer who was caught up in the violence near the Egyptian parliament, said: "We're fed up with Hosni Mubarak. He leads a very rotten government. They are a treacherous government, but control all of the country. The people have no freedom – nothing at all."