Egyptian President Hosni Mubarak, after days of mounting protests against his rule, announced on state television that he would not stand for re-election in September.

He was speaking after a day of dramatic scenes in which hundreds of thousands of people gathered in central Cairo in the biggest demonstration in more than a week of anti-government protests.

There were scenes of defiance in Cairo's Tahrir Square during Mr Mubarak's announcement. The crowd booed and waved shoes chanting: "Go, go, go."

Protesters say they are fed up after decades of poverty, repression, rigged elections, corruption, and high unemployment under Mr Mubarak

Organisers had called for a million-strong march in Cairo, but there were also demonstrations in Egypt's second-city Alexandria and elsewhere.

As in other days since the protests began, the curfew at 1500 local time (1300 GMT) was ignored.

The protesters at Tahrir Square include men, women and children. BBC correspondents at the scene have described a carnival-like atmosphere, with protesters singing and chanting.

Egypt's powerful army has said it will not use force against the people.

But the military is out in force in Cairo, guarding important institutions such as Egypt's national television building.

Despite the massive crowd in Tahrir Square calling for Mr Mubarak to step down, some people in Cairo expressed their support for the president.

While protests in recent days have been largely peaceful, earlier clashes between demonstrators and police may have resulted in 300 deaths, according to the UN's human rights chief.