Harare, Zimbabwe (CNN) Zimbabwe's Parliament has begun impeachment proceedings against President Robert Mugabe, the first time in the country's 37-year history that it has attempted such a move.

A joint sitting of the Senate and National Assembly began after Parliament opened a session earlier Tuesday to lay out the procedures.

The ruling party, ZANU-PF, said it planned to move a motion to formally expel Mugabe, who has been clinging on to the presidency despite a military takeover last week.

ZANU-PF, which Mugabe co-founded and led for decades, ousted the 93-year-old leader as its party chief on Sunday and gave him an ultimatum to step down in 24 hours or face impeachment.

The former vice president, Emmerson Mnangagwa, has joined those calling for Mugabe to stand down, in his first comments since the President fired him on November 6, triggering the political firestorm.

Key developments

Ministers snub Mugabe: Mugabe called a cabinet meeting for Tuesday morning, but most members didn't show up, state media reported, in a further indication that his authority was ebbing away.

'Mugabe go home': Protesters gathered outside the Houses of Parliament, calling for Mugabe to quit, holding signs reading "Bob resign now" and "Mugabe go home."

Mnangagwa's whereabouts unknown: The former vice president's statement offered no clues about his location. Mnangagwa was named as ZANU-PF's new party chief on Sunday, paving the way for him to contest the 2018 presidential elections.

Photos: Political upheaval grips Zimbabwe Members of Zimbabwe's Parliament celebrate after the resignation of longtime President Robert Mugabe was announced on Tuesday, November 21. Mugabe, 93, had led the country for nearly four decades. His resignation comes six days after military leaders seized control of the nation and placed him under house arrest. Hide Caption 1 of 35 Photos: Political upheaval grips Zimbabwe Protesters call for Mugabe's impeachment near the Parliament building in Harare on November 21. Hide Caption 2 of 35 Photos: Political upheaval grips Zimbabwe Demonstrators protest outside the Parliament building on November 21. Hide Caption 3 of 35 Photos: Political upheaval grips Zimbabwe Jacob Mudenda, the speaker of Zimbabwe's Parliament, presides over a session where a motion was moved to impeach Mugabe. Hide Caption 4 of 35 Photos: Political upheaval grips Zimbabwe A man accused of supporting Mugabe is attacked outside Parliament on November 21. Hide Caption 5 of 35 Photos: Political upheaval grips Zimbabwe People gather to pray for the country in a park near Parliament on November 21. Hide Caption 6 of 35 Photos: Political upheaval grips Zimbabwe Lawmakers meet inside Parliament on November 21. Hide Caption 7 of 35 Photos: Political upheaval grips Zimbabwe Gen. Constantino Chiwenga speaks during a news conference in Harare on Monday, November 20. Military leaders had been in talks with Mugabe over his exit, and Chiwenga said that progress had been made. Hide Caption 8 of 35 Photos: Political upheaval grips Zimbabwe Students from the University of Zimbabwe participate in a demonstration in Harare on November 20. Hide Caption 9 of 35 Photos: Political upheaval grips Zimbabwe Newspapers are held in place with rocks at a newsstand in Harare on November 20. Hide Caption 10 of 35 Photos: Political upheaval grips Zimbabwe At a bar in Harare, people watch Mugabe give a televised address to the nation on Sunday, November 19. Mugabe ended the address without giving his resignation. Hide Caption 11 of 35 Photos: Political upheaval grips Zimbabwe Mugabe meets with generals in Harare on November 19. Hide Caption 12 of 35 Photos: Political upheaval grips Zimbabwe Members of the ruling party ZANU-PF react after the decision to oust Mugabe as party leader on November 19. Hide Caption 13 of 35 Photos: Political upheaval grips Zimbabwe A portrait of Mugabe hangs in the hall of the ZANU-PF headquarters, where delegates met for a special committee on November 19. Mugabe co-founded the party and had been its leader for decades. Hide Caption 14 of 35 Photos: Political upheaval grips Zimbabwe A woman and her daughter look out from their balcony as a crowd of protesters gather on the road leading to the State House in Harare on Saturday, November 18. Hide Caption 15 of 35 Photos: Political upheaval grips Zimbabwe People hold a portrait of Zimbabwe's former vice president, Emmerson Mnangagwa, during a demonstration demanding Mugabe's resignation on November 18. ZANU-PF announced Mnangagwa as its new party leader. He was fired by Mugabe on November 6. Hide Caption 16 of 35 Photos: Political upheaval grips Zimbabwe A soldier greets a citizen during a demonstration on November 18. Hide Caption 17 of 35 Photos: Political upheaval grips Zimbabwe People in Harare react as they see a military helicopter fly overhead during protests against Mugabe on November 18. Hide Caption 18 of 35 Photos: Political upheaval grips Zimbabwe Mugabe, center, arrives to preside over a student graduation ceremony at Zimbabwe Open University on Friday, November 17. It was his first public appearance since the military takeover. Hide Caption 19 of 35 Photos: Political upheaval grips Zimbabwe Mugabe, right, is seen in talks about his future in this image tweeted by Caesar Zvayi, the editor of The Herald newspaper, on Thursday, November 16. Hide Caption 20 of 35 Photos: Political upheaval grips Zimbabwe An armored vehicle is on patrol in Harare on November 16. Hide Caption 21 of 35 Photos: Political upheaval grips Zimbabwe Business continues as usual in Harare as roadside vendors sell vegetables on November 16. Hide Caption 22 of 35 Photos: Political upheaval grips Zimbabwe Members of the military check a gun as they stand atop an armored vehicle parked in Harare's central district on November 16. Hide Caption 23 of 35 Photos: Political upheaval grips Zimbabwe An overview of Harare on November 16. Hide Caption 24 of 35 Photos: Political upheaval grips Zimbabwe A banner of Mugabe remains outside the ZANU-PF headquarters in Harare on November 16. Hide Caption 25 of 35 Photos: Political upheaval grips Zimbabwe An armored vehicle patrols a street in Harare on Wednesday, November 15. In a dramatic televised statement, an army spokesman denied that a military takeover was underway, but the situation bore all the hallmarks of one. The military said Mugabe and his family were "safe." Hide Caption 26 of 35 Photos: Political upheaval grips Zimbabwe Soldiers seal off a main road to the parliament building in Harare on November 15. Hide Caption 27 of 35 Photos: Political upheaval grips Zimbabwe Soldiers patrol a street in Harare on November 15. Hide Caption 28 of 35 Photos: Political upheaval grips Zimbabwe Soldiers inspect a vehicle on a road leading to Mugabe's office in Harare on November 15. Hide Caption 29 of 35 Photos: Political upheaval grips Zimbabwe Residents in Zimbabwe's capital line up to withdraw money from a bank on November 15. Hide Caption 30 of 35 Photos: Political upheaval grips Zimbabwe Two pedestrians pass behind an armored personnel carrier stationed at an intersection in Harare on November 15. Hide Caption 31 of 35 Photos: Political upheaval grips Zimbabwe A man in Harare reads a special edition of The Herald newspaper on November 15. Hide Caption 32 of 35 Photos: Political upheaval grips Zimbabwe An armored military vehicle is seen outside the building of the state-run Zimbabwe Broadcasting Corp. on November 15. Hide Caption 33 of 35 Photos: Political upheaval grips Zimbabwe Soldiers monitor traffic in Harare on November 15 as the military set up checkpoints at key locations in the city. Hide Caption 34 of 35 Photos: Political upheaval grips Zimbabwe In a screen grab of a TV broadcast on the Zimbabwe Broadcasting Corp., Maj. Gen. Sibusiso Moyo reads a statement saying the military was conducting an operation to target "criminals" close to the President who were causing "social and economic suffering." He denied a coup was underway. Hide Caption 35 of 35

'The Crocodile' resurfaces

In a TV broadcast on Monday night, the leaders of Zimbabwe's military takeover said Mnangagwa had been in touch with Mugabe and planned to return to the country to discuss the way forward.

But in a a strongly worded statement from an unknown location on Tuesday morning, Mnangagwa said that he would not return until his safety could be guaranteed.

Mnangagwa -- known as "The Crocodile" on account of his sharp political skills -- enjoys widespread support within the military and is reported to have been in touch with army chiefs behind the scenes in recent days. But the apparent divergence in strategy indicated that they may not be moving in lock step.

"I told the President I would not return home now until I am satisfied of my personal security, because of the manner and treatment given to me upon being fired," he said in the statement.

He alleged "friendly" security personnel told him in November there were plans to "eliminate" him once he had been removed from his post.

Mnangagwa called on Mugabe to quit, and launched a thinly veiled attack on the President's cabal. "My desire is to join all Zimbabweans in a new era where corruption, incompetency, dereliction of duty and laziness, social and cultural decadency is not tolerated," he said.

His comments could be interpreted as referring to Mugabe's wife, Grace, whose lavish lifestyle and political ambitions alarmed sections of the ruling party's elite.

Mugabe's efforts to ease Mnanagawa out of the picture and position his wife as his anointed successor were a significant factor in the crisis. Six days after the military takeover, her whereabouts were still unknown.

'Time to go'

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Thousands of protesters gathered outside parliament in Harare on Tuesday in support of Mugabe's impeachment, holding signs reading "Mugabe go home" and "Bob resign now."

At one point, protesters tried to storm the building, in frustration at what is becoming a long drawn-out process.

Others were more patient.

"We've waited for 37 years, we will do whatever it takes to make sure that he goes. So one more day or one more week is not going to make a difference," said Evan Mawarire, a pastor and activist, who described the moves to oust Mugabe as an exciting moment not to be missed.

"The fact is this -- the military has spoken, the people have spoken, parliament spoken, his own party has spoken. So, there's nothing left, he's all by himself."

Such protests are rare in Zimbabwe, where people had for decades been too afraid to protest under the country's oppressive rule.

But ten of thousands of people have shown up to rallies in the capital in recent days in support of the military's actions. Very few have voiced support for Mugabe, and foreign leaders also appear to be tacitly supporting moves to oust him.

On Monday, students at the University of Harare gathered to call for an end to Mugabe's rule, but they were wary of Mnangagwa, a man with a similar history to Mugabe's.

"We might be replacing a snake with another snake, that much ... we know," one student said. "What we're saying is we need new blood as our leader."