The explosion happened close to Mnangagwa as he left the stage in the company of vice-presidents Constantino Chiwenga and Kembo Mohadi.
Mnangagwa was unscathed, but Mohadi suffered a leg injury and Chiwenga’s wife Marry was also injured.
Other senior government officials that were injured in the melee were Zanu PF chairperson Oppah Muchinguri-Kashiri and the party’s commissar Engelbert Rugeje.
A senior government official last night said between eight and nine people were injured.
Mnangagwa, who visited the victims at the Catholic Church-run Mater Dei Hospital, condemned the blast, saying it was a “cowardly act.”
“This afternoon, as we were leaving a wonderful rally in Bulawayo, there was an explosion on the stage,” the president said in a statement posted on his Facebook page.
“Several people were affected by the blast, and I have already been to visit them in hospital.
“While we await further information, my thoughts and prayers are with all those affected by this senseless act of violence.”
He said the alleged attack will not stand in the way of free and fair elections.
“The campaign so far has been conducted in a free and peaceful environment, and we will not allow this cowardly act to get in our way as we move towards elections,” Mnangagwa said.
“Let us continue to be united and address our differences peacefully. “The strongest response to violence is peace. The strongest response to hate is love.”
Mnangwa’s spokesperson George Charamba said eight people, including the senior government officials were injured in the blast.
“Minister Muchinguri-Kashiri is still in a state of shock and she has some injuries around her chest,” he told state-controlled media last night.
“National commissar General Rugeje had some shrapnel in his arm, but he has been attended to and discharged.
“Mai Chiwenga had some lacerations on her face as she tried to rescue one of her aides who had shrapnel in her stomach.
“VP Chiwenga has slight bruises on his face but he is fine. Four security personnel and some chiefs were also injured so all in we are talking of eight to nine people who have been injured.”
The blast blew off the staircase soon after Mnangagwa touched the ground, and several security aides and Zanu PF officials could be seen lying down injured.
Two security aides could be seen lying on the ground motionless soon after the blast.
After the injured senior government officials arrived at Mater Dei, the private hospital was sealed off by the presidential guard.
Former War veterans minister Tshinga Dube who sat on the main stage with Mnangagwa said they were shaken by the incident.
“We just don’t know what happened,” he said soon after the incident.
“It all happened in a split second and all we could see was smoke, and the stampede at the high table resulting in some injuries.”
Dube was left nursing an injured knee.
Meanwhile, there was pandemonium at the stadium after the blast as people scurried for cover.
Zanu PF supporters, police, journalists and other security details ran for dear life as panic set in.
Central Intelligence Organisation operatives tried to force photojournalists to delete pictures taken after the blast.
In the ensuing melee, the presidential guard — also caught unawares — moved to cordon off the area, while telling everyone to vacate the scene.
Mnangagwa had started his address at the rally by referring to an alleged plot to kill him by former president Robert Mugabe’s allies at the height of the Zanu PF succession wars last year.
“Before I address you today, I want to remind you what happened on 4 November last year,” he said.
“You all remember what happened. I had no hand in the booing of the former first lady (Grace Mugabe). However, I was accused of sponsoring the booing.
“After being insulted I thanked the former first lady for insulting me.
“The former president then told me that I would be fired the following day and it happened like that.”
Mnangagwa said Mugabe offered him refuge at his home after he escaped to South Africa, but he told him that people around the 94-year-old wanted to kill him.
Before last year’s rally at White City Stadium where the booing incident took place, Mnangagwa was allegedly poisoned during a Zanu PF rally in Gwanda.