Two people injured in Saturday's explosion at a campaign rally in Zimbabwe's second city of Bulawayo have died, a medical official has said.

Solwayo Ngwenya, clinical director of the city's Mpilo hospital in the city, told AFP other victims had life-threatening injuries.

At least 49 people, including President Emmerson Mnangagwa's two deputies, were injured in the blast.

He said it was an attempt on his life ahead of the 30 July election.

This is the first poll since long-time leader Robert Mugabe was forced from power last year.

Mr Mnangagwa has vowed that the attack would not derail the election.

He is favourite to win the poll, but analysts say he also has enemies - both for overthrowing his former mentor, and for being a previous enforcer of Mr Mugabe's government.

His main rival, Nelson Chamisa, has also condemned the attack, for which there has been no claim of responsibility.