Protesters are celebrating in Egypt as Hosni Mubarak steps down as president, ending three decades of autocratic rule.

After 18 days of mass protests, anti-government demonstrators are overjoyed as power has been handed over to the army.

A speaker made the announcement in Cairo's Tahrir Square, where hundreds of thousands of people broke down in tears.

The crowd have been chanting: "The people have brought down the regime." Others shouting: "Allahu Akbar'' meaning God is great.

Vice President Omar Suleiman said a military council would run the affairs of the Arab world's most populous nation. A free and fair presidential election has been promised for September.

The 82-year-old former president's downfall after unprecedented mass protests is a momentous victory for people power and will be likely to rock autocrats throughout the Arab world and beyond.

Demonstrators have been angered by President Mubarak's announcement on Thursday that he will not step down.