Several security personnel were also injured, the state-owned Herald newspaper said.

Footage from Zimbabwe state television showed that the explosion took place near Mr. Mnangagwa as he waved to supporters. He was later seen, in pictures on social media, visiting Mr. Chiwenga’s wife in the hospital.

Mr. Mnangagwa, 75, was speaking at his first rally in Bulawayo, an opposition stronghold where the governing ZANU-PF has not won in national elections since 2000.

Zimbabwe holds its election on July 30, with Mr. Mnangagwa and Nelson Chamisa — the leader of the opposition Movement for Democratic Change — as the main contenders for the presidency.

Next month’s vote is the first since Robert Mugabe was ousted in a coup last November.

Unlike previous elections, which were marred by violence — mostly against opposition members by ZANU-PF supporters — the run up to this year’s vote had been relatively peaceful.