Tanks have been spotted heading towards Zimbabwe’s capital Harare, according to a report in the Independent.
Eyewitnesses also report that military vehicles were blocking major roads outside the city.
Local media also reported that heavily armed military personnel had sealed off state TV broadcaster ZBC.
It comes after Zimbabwe’s top general warned that the military would not hesitate to step in to end purges against former liberation war fighters including Mr Mnangagwa, who is known as the “crocodile” because of his perceived shrewdness.
“We must remind those behind the current treacherous shenanigans that, when it comes to matters of protecting our revolution, the military will not hesitate to step in,” said General Constantino Chiwenga in a statement.
“The current purging … targeting members of the party with a liberation background must stop forthwith”.
The commander of Zimbabwe Defence Forces and political ally of Mr Mnangagwa, added that the Zanu-PF had been hijacked by people who did not fight in the 1970s liberation war, which some commentators read as a criticism of Ms Mugabe, a vocal critic of the former vice president.
In response, the party’s Youth League accused the military chief of subverting the constitution.
“We will not fold out hands to allow a creature of the constitution to subvert the very constitution which establishes it,” said Kudzai Chipanga.
“Defending the revolution and our leader and president is an ideal we live for and if need be it is a principle we are prepared to die for,” he added.
The rising political tension in comes at a time when it is struggling to pay for imports due to a dollar crunch, which has also caused acute cash shortages.
Zimbabwe’s state media refrained from publishing General Chiwenga’s statement.
The Herald newspaper, which had initially posted some of his comments on its official Twitter page, deleted the posts without explanation.