An explosion rocked a stadium where Zimbabwe's president was addressing a campaign rally on Saturday in what state media have called an assassination attempt.

Footage showed a blast just as President Emmerson Mnangagwa, nicknamed The Crocodile, had just finished addressing the crowd and was leaving the podium.

Mnangagwa was whisked to safety a state house in the city of Bulawayo, where he had been speaking ahead of next month's election.

He later called for unity despite political differences after 'this senseless act of violence' and said he would not allow a 'cowardly act to get in our way as we move towards elections'.

The country's vice president Constantino Chiwenga and his wife sustained minor injuries from the blast at the White City Stadium, a source close to the president said.

Footage showed the explosion at a rally where the Zimbabwean President was speaking

Injured people lie on the ground following an explosion at the rally in Bulawayo today

Footage posted online showed the president waving to the crowd, turning to step off the podium and walking into the open-sided VIP tent.

Seconds later the explosion occurred before people ducked and screamed and smoke billowed.

Several people appeared to be injured, and footage showed medical staff rushing to the scene. State television immediately cut its broadcast.

Presidential spokesman George Charamba said: 'There has been an incident at Bulawayo where the president was addressing a rally.

This is now a police issue but the president is safe at Bulawayo State House.

'We are still to get information on what exactly happened as we understand that some people could have been injured as this happened in the VIP tent.'

He told The Zimbabwe Herald that investigations were underway, and pointed out that there have been 'multiple attempts' on Mnangagwa's life over the years.

The U.S. Embassy said on Twitter that 'political violence in any form is unacceptable' and contrary to the progress needed to move the country forward and 'take its place on the global stage.'

The British Embassy has tweeted a similar statement, saying there is 'no place for any form of political violence in Zimbabwe'.

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.

Members of the Zimbabwe Red Cross Society carry an injured member of the Zimbabwe National Army after the explosion at the White City Stadium

President Emmerson Mnangagwa was safely at a state house in the city of Bulawayo, where he had been speaking ahead of next month's election, a spokesman said

Members of the Zimbabwe African National Union - Patriotic Front (ZANU-PF) shield Zimbabwean vice president Constantine Chiwenga away after the bomb went off

Mnangagwa took power in November after his former ally, longtime leader Robert Mugabe, stepped down under military pressure.

The July 30 election will be the first without Mugabe in the southern African nation since independence in 1980.

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.

Bulawayo, Zimbabwe's second-largest city, is traditionally an opposition stronghold.