The army said it was securing government offices and patrolling the capital’s streets, after a night of unrest which included a military takeover of the state broadcaster.
The action triggered speculation of a coup, but the military’s supporters praised it as a “bloodless correction”.
“We wish to make it abundantly clear that this is not a military takeover,” Zimbabwe Major General SB Moyo, Chief of Staff Logistics, said on television.
“We are only targeting criminals around [Mr Mugabe] who are committing crimes that are causing social and economic suffering in the country in order to bring them to justice.
“As soon as we have accomplished our mission, we expect that the situation will return to normalcy.”
Neither Mr Mugabe nor his wife Grace, who has been vying to succeed her husband as president, have been seen or heard from.
At least three explosions were heard in the capital, Harare, overnight, and military vehicles were seen in the streets.
The US Embassy closed to the public on Wednesday and encouraged citizens to shelter in place, citing “the ongoing political uncertainty through the night.”
The British Embassy issued a similar warning, citing “reports of unusual military activity.”