Mnangagwa confirmed today that an object "exploded a few inches away from me". "The country is peaceful".
One of Zimbabwe's two vice presidents, Kembo Mohadi, suffered a leg injury in the blast, which happened in Bulawayo.
The explosion was close to the VIP tent, they said.
"President Mnangagwa has not been injured and is at Bulawayo State House".
He was later seen in pictures circulating on social media visiting Chiwenga's wife in hospital.
However three were seriously injured.
Emmerson Mnangagwa, the president of Zimbabwe, called for peace, love and unity in the small southern African state last night, hours after escaping an apparent assassination attempt during an election campaign rally in the southern city of Bulawayo. Violence must have no place in our politics'. "So far, we had avoided the violence that has marred previous elections".
Spokesman George Charamba said investigations were underway and that there have been "multiple attempts" on Mnangagwa's life over the years.
He spent weeks receiving medical treatment in neighbouring South Africa. Mnangagwa, a former justice and defense minister who served for decades as Mugabe's enforcer, has invited Western election observers for the first time in nearly two decades.
Both main candidates are campaigning on a pledge to revive an economy crippled by a legacy of often violent seizures of land from white commercial farmers and a black economic empowerment drive that targeted foreign-owned businesses.
Other injured officials included Oppah Muchinguri-Kashiri, minister of water, environment and climate, and Engelbert Rugeje, party secretary of the ruling ZANU-PF.