Zimbabwe's military has told regional leaders its move to seize power from President Robert Mugabe and take over his Government's institutions is "not a coup d'etat", regional officials say.

Key points: Military says it is keeping Mr Mugabe safe while rounding up "criminals"

Military says it is keeping Mr Mugabe safe while rounding up "criminals" Reports that Mr Mugabe's wife Grace has fled to neighbouring Namibia

Reports that Mr Mugabe's wife Grace has fled to neighbouring Namibia UN chief, world leaders call for fundamental rights to be respected

"The military have reassured us this is not a coup d'etat," Moussa Faki Mahamat, the head of the African Union Commission, said.

"The African Union is against any unconstitutional change of government."

Soldiers seized the state broadcaster yesterday and a general appeared on television to announce the takeover, as armoured vehicles blocked roads to main government offices, Parliament, and the courts.

In the televised statement, Zimbabwe's military said it was keeping Mr Mugabe and his wife Grace "safe and sound" while targeting "criminals" in the entourage of the only ruler the country has known in its 37 years of independence.

"We are only targeting criminals around him [Mugabe] who are committing crimes that are causing social and economic suffering in the country in order to bring them to justice," military spokesman Major General SB Moyo said.

"As soon as we have accomplished our mission, we expect that the situation will return to normalcy."

The "criminals" reportedly include various government officials, including the country's Finance Minister, Ignatius Chombo.

In his first contact with the outside world since the takeover, Mr Mugabe spoke by telephone to South African President Jacob Zuma and told him he was confined to his home but fine, the South African presidency said in a statement.

Military vehicles and soldiers patrol the streets in Harare. ( Reuters: Philimon Bulawayo )

Mr Zuma said he was sending his ministers of defence and state security to Zimbabwe to meet with Mr Mugabe and the military.

He said he hoped Zimbabwe's army would respect the constitution and that the situation was "going to be controlled".

World leaders call for 'calm, non-violence, restraint'

Meanwhile, United Nations Secretary-General Antonio Guterres and leaders from around the world have appealed for calm and restraint in Zimbabwe amid the crisis.

"The UN Secretary-General is monitoring the evolving situation in Zimbabwe," UN spokesman Farhan Haq said.

"He appeals for calm, non-violence and restraint. Preservation of fundamental rights, including freedom of speech and assembly, is of vital importance."

Sorry, this video has expired Soldiers and army tanks are seen just outside the capital, Harare (Photo: Reuters/Philimon Bulawayo)

British Foreign Secretary Boris Johnson said it was not clear whether the dramatic events in Zimbabwe marked "the downfall of Mugabe".

Mr Johnson accused Mr Mugabe of rigging elections, torturing opponents and "the worst hyper-inflation in recorded history", and said the country must not exchange one "unelected tyrant" for another.

The African Union Commission said it was crucial the political crisis be resolved in a manner that promoted democracy and human rights — the commission was closely following developments in Harare, Mr Faki said.

Citizens carry on with daily lives

People continue with their lives as the army controls the streets of Harare. ( AP )

The whiplash developments followed Mr Mugabe's firing last week of his deputy, which appeared to position the first lady, Grace Mugabe, to replace Emmerson Mnangagwa as one of the country's two vice presidents at a party conference next month.

Mr Mnangagwa's whereabouts were not clear on Wednesday. He fled the country last week, citing threats to him and his family.

As the military took control of the capital and the state broadcaster, it appeared more and more likely the world's oldest head of state was being deposed by a coup — the army's supporters praised the move as a "bloodless correction".

Former VP Emerson Mnangagwa (right) was removed from office last week amid attacks from Grace Mugabe (left). ( Reuters: Philimon Bulawayo, file )

Citizens in the capital, Harare, contributed to the feeling of a smooth change by carrying on with their daily lives, walking past the army's armoured personnel carriers to go to work and to shops.

Many who have never known any leader but Mr Mugabe waited in long lines at banks to draw limited amounts of cash, a result of this once-prosperous country's plummeting economy.

"I am just following what is happening on WhatsApp but I am still in the dark about what is happening," said Felix Tsanganyiso, who sells mobile airtime vouchers.

"So far so good; we are going about our business without harassment.

"My plea is that whoever takes over should sort out the economy. We are tired of living like this."

Critics of the Government urged Mr Mugabe to go quietly.

"The old man should be allowed to rest," former Zimbabwe finance minister and current activist Tendai Biti told South African broadcaster eNCA.

A street scene along Robert Mugabe road in Harare. ( AP: Tsvangirayi Mukwazhi) )

Reuters/AP