Zimbabwean President Robert Mugabe has resigned, the country's parliamentary speaker has said.

The announcement came as the parliament was beginning impeachment proceedings against Zimbabwe's leader.

There were celebrations in the chamber as Mr Mugabe's resignation letter was read out.

The veteran leader said he had chosen to step down "to allow the smooth transfer of power" and had made the decision voluntarily.

The announcement has sparked jubilant scenes in the capital Harare, where protesters had gathered to call for the 93-year-old to be removed from office.

Mugabe held his last cabinet meeting this morning - which just five ministers attended.

He had stunned his country on Sunday when he failed to announce that he was stepping down.

An ultimatum from his Zanu-PF party to resign by midday on Monday or face impeachment also came and went with no word from Mr Mugabe.

The party decided to press ahead with impeachment by tabling a motion, which it was believed could have been passed within days.

Mugabe has ruled Zimbabwe with an iron fist since 1980, but has seen his rule challenged over the last week.

The sacking of vice president Emmerson Mnangagwa put Mugabe's unpopular wife, Grace, in prime position to succeed the veteran leader.

The army promptly seized power and put Mr Mugabe under house arrest - but insisted it had not staged a coup.