Police spokesperson Charity Charamba said "comprehensive investigations are in progress at the crime scene" at the White City Stadium in the second largest city Bulawayo.
"All expert teams are now firmly on the ground conducting investigations," Charamba said on Sunday.
She said 49 people were injured in the explosion that took place as Mnangagwa left an election campaign rally on Saturday.
“We expect the number to rise as some victims might come forward during the course of the day,” she told journalists.
Charamba said the police are offering undisclosed reward to anyone with information on the people or group behind the blast.