Video footage from White City Stadium appears to show an explosion happening close to Mr Mnangagwa as he was leaving the stage having addressed supporters.
While the president was unhurt, state TV reports that Vice-President Kembo Mohadi has suffered a leg injury.
[ads1]President Mnangagwa came into power last November, ousting his former mentor Robert Mugabe.
The president was in Bulawayo, Zimbabwe’s second city, to campaign for his Zanu-PF party ahead of nationwide elections taking place on 30 July.
The elections are the first in Zimbabwe since Mr Mugabe was ousted after 37 years in power.
Presidential spokesman George Charamba issued a statement confirming Mr Mnangagwa was safe and recalling: “There have been multiple attempts on the president’s life over the past five years.”
It is not clear how severe the injuries to Second Vice-President Kembo Mohadi are.
Zimbabwe’s First Vice-President, Constantino Chiwenga, and his wife, suffered minor injuries, Reuters news agency reports.
The Zimbabwe Herald newspaper described the explosion as an assassination attempt on the president.
State broadcaster ZBC also reported that Zanu PF national chairman Oppah Muchinguri-Kashiri and some ZBC crew members were also injured
Source: BBC