An explosion rocked a stadium where Zimbabwe's president was addressing a campaign rally on Saturday, with state media calling it an assassination attempt but saying he was not hurt and was evacuated from the scene. Witnesses said several people were injured, including a vice president.President Emmerson Mnangagwa was whisked to a state house in Bulawayo, where he had been speaking ahead of next month's historic election, the first since longtime leader Robert Mugabe stepped down."Assassination attempt," the state broadcaster said.The blast occurred as Mnangagwa had just finished addressing the crowd and was leaving the podium.Footage posted online showed the president waving to the crowd, turning to step off the podium and walking into the open-sided VIP tent, where seconds later the explosion occurred. People ducked and screamed and smoke billowed.State television immediately cut its broadcast. The broadcaster, ZBC, later reported that Vice President Kembo Mohadi was injured in the leg and taken to a local hospital.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and FacebookThe crowd in the stadium rushed for the exits. Police spokesperson Charity Charamba said she was still verifying the number of injured people.Bulawayo, Zimbabwe's second-largest city, is traditionally an opposition stronghold.The explosion came just hours after a similar attack in Ethiopia, where a blast killed at least one person and injured scores just after the new prime minister addressed a huge rally in the capital.Presidential spokesperson George Charamba told The Zimbabwe Herald that investigations were under way, and pointed out that there have been "multiple attempts" on Mnangagwa's life over the years.The president himself has openly joked about the attempts, including during his campaigning.Mnangagwa took power in November after former ally Mugabe stepped down under military pressure. That dramatic transfer of power began when Mnangagwa was fired as Mugabe's deputy and said he had to immediately flee the country for his life.The July 30 election will be the first without Mugabe in the southern African nation since independence in 1980. Mnangagwa has pledged to hold a free and fair election, inviting Western observers for the first time in almost two decades.Past votes have been marked by allegations of violence and fraud, and the United States and others have said a credible vote is key to lifting international sanctions.