Zimbabwean military officers have read an address live on state TV, saying they were not launching a coup but were "targeting criminals around" President Robert Mugabe.
Zimbabwe's ambassador in South Africa, Isaac Moyo, dismissed any talk of a coup and said the government was "intact".
Witnesses said several state broadcaster ZBC members of staff were manhandled in the early hours of the morning (local time) as the soldiers occupied the premises, while the source of the explosions was not immediately apparent.
But the Zanu-PF party said Chiwenga's comments were meant to "incite insurrection" and that it "reaffirms the primacy of politics over the gun" and accused him of "treasonable conduct".
Tensions were raised further on Tuesday when armoured vehicles were seen taking up positions on roads outside Harare, although their objective was unclear.
There are reports that the military in Harare has said: "We are in control".
The statement from the ZANU-PF party was released amid worries that the military might be taking action to oust Mugabe.
Mugabe has ruled for 37 years but has recently fired veterans of the liberation struggle from party posts, leaving the top of Zanu-PF full of officials who did not fight in the country's independence war.
Soldiers deployed across the Zimbabwe capital Harare on Tuesday and seized the state broadcaster after Mugabe's ruling ZANU-PF party accused the head of the military of treason, prompting frenzied speculation of a coup.
The US embassy in the capital said it would be closed on Wednesday due to the "uncertainty", while advising US citizens to "shelter in place".
Mugabe is at his residence in Borrowdale‚ at his Blue Roof mansion‚ with his wife Grace and is under heavy military guard. Grace Mugabe has developed a strong following in the powerful youth wing.
Mutsvangwa and the war veterans are staunch allies of Emmerson Mnangagwa, who was sacked from his post of vice president by Mugabe last week.
Mugabe's firing of Vice President Emmerson Mnangagwa, his right-hand man for almost four decades, stunned the nation.
"The government's silence on the military deployments seem to confirm that President Mugabe has lost control of the situation", Robert Besseling, of the London-based EXX Africa risk consultancy, said.
The military's intervention came after a period of unrest within Mugabe's ruling Zanu-PF.
Grace Mugabe's rise has brought her into conflict with the independence-era war veterans, who once enjoyed a privileged role in the ruling party under Mugabe, but who have in recent years been banished from senior government and party roles. Apparently referring to Mugabe, the tweet said "an elderly man who had been taken advantage of by his wife [was] detained".