Khuluma Afrika, which describes itself as a centre for investigative journalism and current affairs, reported late on Wednesday that the heightened military presence was to improve security amid rumours of a coup.
According to the centre, Mugabe was not at home and his motorcade was still at his Munhumutapa offices, also in Harare, where secret service personnel were reportedly dispatched.
The cordoning off of ZBC premises was also in line with upped security in the southern African country amid a political impasse, the website said.
Controversial Mugabe has historically tightened personal security, especially over simple things like social media dissent or strikes by workers.
eNCA’s Zimbabwean correspondent Pindai Dube confirmed the tanks were visible in the streets of Harare, with sources indicating it was a ‘show of force’ rather than a coup.
South African Airways spokesperson Tlali Tlali said flights between Zimbabwe and South Africa are continuing as usual.
“Our flights between the two countries are operating as per published schedules. Should there be a change in scheduling, a public and customer notification will be issued,” he added.
Sacked vice-president Mnangagwa, 75, a long-serving veteran of Zimbabwe’s 1970s liberation wars, had been viewed as a likely successor to Mugabe before the president fired him on 6 November.
His downfall appeared to pave the way for Mugabe’s wife, Grace, to succeed the 93-year-old president.
Robert Mugabe is the only leader Zimbabwe has known in 37 years of independence.
Additional reporting by Reuters