Prime Minister Morgan Tsvangirai lost his wife of 30 years in Friday's crash
Zimbabwe PM Morgan Tsvangirai has flown to neighbouring Botswana for medical tests and rest, a day after a car crash which killed his wife, his party says.
A source close to Mr Tsvangirai told the BBC he was exhausted and needed time to come to terms with events.
His MDC party says it will carry out its own inquiry into the cause of the crash. But officials have said nothing to suggest they suspect foul play.
Mr Tsvangirai has previously spent time in Botswana while in opposition.
He returned from Botswana to Zimbabwe on 17 January this year, having spent much of the previous two months away.
The source who spoke to the BBC said the prime minister's departure from Zimbabwe was not because of security concerns.
Mr Tsvangirai, 56, on Saturday afternoon left the Harare clinic where he was treated for head and neck injuries sustained in the crash the previous day.
The AFP news agency quoted an MDC spokesman as saying: "I do not know when he will be back, he will undergo a check-up, but he is out of danger now."
Mr Tsvangirai was on his way to his rural home in Buhera, where he planned to hold a weekend rally, when the crash occurred near Beatrice at about 1600 local time (1400 GMT) on Friday.
Police said a lorry carrying freight crossed into the lane in which the prime minister's 4x4 was travelling and side-swiped the vehicle, causing it to roll over three times.
US embassy officials said the lorry belonged to a partner organisation of the US government aid agency USAID.
The UK Foreign Office confirmed on Saturday that the lorry was operated by a project jointly funded by the US and UK.
"All indications are that this was a genuine accident," a Foreign Office spokeswoman said.
Mr Tsvangirai and his wife Susan, 51, who married in 1978, had six children.
Friends and relatives gathered at the Tsvangirai family home on Saturday to console one another for her loss.
The crash came just two days after Mr Tsvangirai delivered his maiden speech to parliament after being sworn in as prime minister in Zimbabwe's power-sharing government.
He was visited in hospital by his political rival President Robert Mugabe and his wife Grace.
The Tsvangirais' vehicle rolled several times
But relations between the MDC and Mr Mugabe's Zanu-PF party remain tense, with MDC ministerial nominee Roy Bennett still in custody, accused of links to an alleged plot to kill Mr Mugabe.
MDC secretary-general Tendai Biti paid tribute to Mrs Tsvangirai on Saturday, calling her "a mother to us and to our struggle".
Speaking at a news conference, he said the accident could have been avoided if a police escort had been provided.
"Logic would have demanded that a police escort be provided to the prime minister to warn other traffic and this tragedy could have been avoided," he said.
However, correspondents point out that Mr Tsvangirai was not entirely comfortable with security provided by the new government, relying instead on his own security teams.
Mr Biti said police investigations were under way but said the party would carry out its own independent investigation.
All Zimbabwe's roads are in a poor state of repair after years of neglect, correspondents say.
Another MDC official, Nelson Chamisa, said the party considered the crash to have been an accident, but that it had been decided to increase security around Mr Tsvangirai, the BBC's Peter Biles in Johannesburg reports.
In the face of personal tragedy, Mr Tsvangirai now faces a mammoth task in consolidating his role as Zimbabwe's new prime minister in a power-sharing government, our correspondent says.