According to BBC, the military has seized control in Zimbabwe but has said President Robert Mugabe, in power since 1980, is safe.
After seizing state TV, an army spokesman announced it was targeting people close to Mr Mugabe who had caused "social and economic suffering".
The move came after Mr Mugabe sacked his deputy, Emmerson Mnangagwa, in favour of his wife, Grace.
Heavy gun and artillery fire could be heard in northern parts of the capital Harare early on Wednesday.
A statement read out by a general on air denied it was a coup. There was no immediate word from the president himself.
Mr Mugabe, 93, has dominated the impoverished country's political scene since independence from the UK.
The UK Foreign Office advised Britons "currently in Harare to remain safely at home or in their accommodation until the situation becomes clearer", while the US embassy in Harare advised US citizens in Zimbabwe to "shelter in place" until further notice.
How did the military justify its move?
Troops in armoured vehicles have been out in the streets of the capital Harare since Tuesday.
After soldiers overran the headquarters of the ZBC broadcaster, Maj Gen Sibusiso Moyo went on air to say the military wished to "assure the nation that his Excellency the president... and his family are safe and sound and their security is guaranteed".
Soldiers patrolled Harare on Wednesday
"We are only targeting criminals around him who are committing crimes... that are causing social and economic suffering in the country," he said.
"As soon as we have accomplished our mission, we expect that the situation will return to normalcy."
Other key points of the statement included:
Citizens should remain calm and limit unnecessary movement
The military assures the Zimbabwean judiciary that its independence is guaranteed
Security services should "co-operate for the good of our country" and any provocation would "be met with an appropriate response"
All leave for the defence forces is cancelled and personnel should return to barracks immediately
It is not clear who is leading the military action. Army chief Gen Constantino Chiwenga had said the army was prepared to act to end purges within the ruling Zanu-PF party.
What do we know of the shooting?
The firing was coming from northern suburbs where Mr Mugabe and a number of government officials live, the BBC's Shingai Nyoka reports from Harare.
A witness told AFP news agency it could be heard near Mr Mugabe's residence in the suburb of Borrowdale early on Wednesday,
Some staff at ZBC were manhandled when the soldiers moved in, sources told Reuters.
Has anyone been detained?
A government source told Reuters news agency that Finance Minister Ignatius Chombo had been detained.
He is a leading member of a faction of Zanu-PF led by Grace Mugabe.
Is this a coup?
Alex Magaisa, former adviser to Zimbabwean opposition leader Morgan Tsvangirai, told the BBC: "They have decided not to call it a coup because they know that a coup does not sell, it will be condemned.