Tsvangirai was the opposition leader who was made Mr Mugabe's deputy
Zimbabwe's defeated former prime minister has returned to the country as politicians eye opportunities for power while President Robert Mugabe is under house arrest.
Morgan Tsvangirai was the opposition leader who was made Mr Mugabe's deputy between 2009 and 2013 after he saw a surge in support in elections.
Reports say two other government ministers have also returned to their country from Russia.
It came after the army seized power in the country in what the leader of the African Union said looked like a "coup".
Mr Mugabe is being detained in the presidential palace, where explosions and gunshots were heard early on Wednesday.
The army said it was holding the president and his wife Grace, but there have also been rumours she had fled to Namibia.
Earlier, African Union leader Alpha Conde, said: "The African Union expresses its serious concern regarding the situation unfolding in Zimbabwe."
He went on to insist that "constitutional order... be restored immediately" and called "on all stakeholders to show responsibility and restraint".
United Nations Secretary-General Antonio Guterres appealed for calm, non-violence and restraint after gunfire and explosions were heard near Mr Mugabe's compound.
On Monday, the head of the armed forces had warned that a "purge" of government political figures who had taken part in the 1970s wars of independence had to "stop".
The sacking of the vice president and Mr Mugabe's likely successor Emmerson Mnangagwa, last week, was seen as clearing the way for Mrs Mugabe to take over from her husband, after she won the support of ZANU-PF's youth wing.
The military said it was taking control of the streets, blocking roads to the parliament and court to target "criminals".
The head of the youth wing of Zimbabwe's ruling party appeared on state television on Wednesday night, to apologise to the military.
Kudzai Chipanga said he had voluntarily given his statement apologising for denigrating defence forces chief General Constantino Chiwenga.
The Irish embassy in Pretoria is monitoring events in Zimbabwe.
It has advised Irish citizens to remain indoors and to avoid areas where demonstrations may be taking place.
It has also set up emergency numbers for Irish citizens to call:
Please note the phone lines at the Embassy are currently down -in case of emergency please contact +27792565946 or +27824599863.— IrishEmbassyPretoria (@IrlEmbPretoria) November 15, 2017