Zimbabwe President Robert Mugabe has defied expectations he would resign, pledging to preside over a ZANU-PF party congress next month even though the ruling party has removed him as its leader.

ZANU-PF had given the 93-year-old less than 24 hours to quit as head of state or face impeachment - an attempt to secure a peaceful end to his tenure after a de facto coup.

Mr Mugabe said in a address on state television that the events of the past week were not a threat to his authority as head of state and commander in chief, or the constitution.

He acknowledged criticism against him from ZANU-PF, the military and the public, but did not comment on the possibility of standing down.

Mr Mugabe said he was aware of the range of concerns that the citizens of Zimbabwe have, adding that his meeting today with military commanders underscored the need to collectively start processes that return the nation to normalcy.

He said that the people need peace, security, law and order.

Chris Mutsvangwa, the leader of the liberation war veterans who have been spearheading an 18-month campaign to oust Mr Mugabe, said plans to impeach him in parliament, which sits on Tuesday, would now go ahead, and that there would be mass protests on Wednesday.

He also implied that Mr Mugabe, who spoke with a firm voice but occasionally lost his way in his script during the 20-minute address, was not aware of what had happened just hours earlier.

"Either somebody within ZANU-PF didn't tell him what had happened within his own party, so he went and addressed that meeting oblivious, or (he was) blind or deaf to what his party has told him," Mr Mutsvangwa said.

Zimbabwe opposition leader Morgan Tsvangirai said he was "baffled" by Mr Mugabe's address. 

"I am baffled. It's not just me, it's the whole nation. He's playing a game. He has let the whole nation down," he said.

Zimbabwe's ruling party earlier fired Mr Mugabe as its leader.

Mr Mugabe, the only leader the southern African nation has known since independence from Britain in 1980, was replaced by Emmerson Mnangagwa, the deputy he sacked this month in a move that triggered Tuesday's intervention by the army.

Delegates at this morning's special meeting of Mr Mugabe's ZANU-PF party

In scenes unthinkable just a week ago, the announcement of his firing as leader was met by cheers from the 200 delegates packed into ZANU-PF's Harare headquarters, whose support has crumbled in the four days since the army seized power.

Mr Mugabe was given until noon tomorrow to resign or face impeachment, an ignominious end to the career of the "Grand Old Man" of African politics who was once feted across the continent as an anti-colonial liberation hero.

As the vote was announced, Mr Mutsvangwa, who has spearheaded an 18-month campaign to remove a man he openly described as a "dictator", embraced colleagues and shouted: "The President is gone. Long live the new President."

"He has been expelled," one of the delegates said. "Mnangagwa is our new leader."

Mr Mugabe's wife Grace, who had harboured ambitions of succeeding Mr Mugabe, was also expelled from the party.

Speaking before the meeting, Mr Mutsvangwa said Mr Mugabe, 93, was running out of time to negotiate his departure and should leave the country while he could.

"He's trying to bargain for a dignified exit," he said.

Mr Mutsvangwa followed up with a threat to call for street protests if Mr Mugabe refused to go, telling reporters: "We will bring back the crowds and they will do their business."

Mr Mnangagwa, a former state security chief known as "The Crocodile", is now in line to head an interim post-Mugabe unity government that will focus on rebuilding ties with the outside world and stabilising an economy in freefall.

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Yesterday, hundreds of thousands of people flooded the streets of Harare, singing, dancing and hugging soldiers in an outpouring of elation at Mr Mugabe's expected overthrow.

His stunning downfall in just four days is likely to send shockwaves across Africa, where a number of entrenched strongmen, from Uganda's Yoweri Museveni to Democratic Republic of Congo's Joseph Kabila, are facing mounting pressure to quit.

Men, women and children ran alongside the armoured cars and troops who stepped in this week to oust the man who has ruled since independence from Britain in 1980.

Under house arrest in his lavish 'Blue Roof' compound, Mr Mugabe has refused to stand down even as he has watched his support from party, security services and people evaporate in less than three days.

His nephew, Patrick Zhuwao, told Reuters that Mr Mugabe and his wife were "ready to die for what is correct" rather than step down in order to legitimise what he described as a coup.

But on Harare's streets, few seemed to care about the legal niceties as they heralded a "second liberation" for the former British colony and spoke of their dreams for political and economic change after two decades of deepening repression and hardship.

The huge crowds in Harare have given a quasi-democratic veneer to the army's intervention, backing its assertion that it is merely effecting a constitutional transfer of power, rather than a plain coup, which would entail a diplomatic backlash.