Ohio police officers in Wisconsin for the Republican National Convention shot and killed a man who was wielding two knives near the convention, Milwaukee's police chief has said.

Five members of the Columbus, Ohio, police department fired on the man, who had a knife in each hand, refused police commands and charged at an unarmed man before police fired, Milwaukee Chief Jeffrey Norman said at a news conference on Tuesday. Two knives were recovered from the scene, the chief said.

“Someone's life was in danger,” Norman said. “These officers, who were not from this area, took it upon themselves to act and save someone's life today.”

Thousands of officers from multiple jurisdictions are in Milwaukee providing additional security for the convention that began Monday and concludes Thursday.

The shooting fuelled anger from residents who questioned why out-of-state officers were in their neighbourhood located about a mile from the convention site.

The Columbus Police Department, as well as the chief of staff for Milwaukee's mayor and a spokesperson for the convention's joint command centre, all said there was nothing to suggest the shooting was related to the convention itself.

Milwaukee residents and activists quickly converged on the site of the shooting, many of them expressing outrage about the involvement of a police department in town because of the convention. They planned a nighttime vigil.

“They came into our community and shot down our family right here at a public park,” said Linda Sharpe, a cousin of the man who was killed. “What are you doing in our city, shooting people down?”

Sharpe said her cousin, who she identified as Samuel Sharpe, lived in a tent encampment across the street from King Park, where the shooting occurred.

Residents said the encampment was a long-standing feature of the neighbourhood, which is home to several social service clinics and a shelter. Some said Milwaukee police officers are familiar with many of those living in the tents and might have been able to deescalate the situation.

Kenneth Johnson, a volunteer with Friends Without Shelter, said he often dropped off food to the man and others who lived in the tents — and questioned what an out-of-state officer had been doing at the location.

David Porter, who said he knew the man and is also homeless, was angry that officers from outside of Milwaukee were in his neighbourhood.

“If MPD would have been there, that man would still be alive right now,” Porter said, referring to Milwaukee police.

Norman, the Milwaukee chief, said 13 officers who were part of a bicycle patrol from Columbus were within their assigned zone having a meeting when they saw the altercation.

“The officers observed a subject armed with a knife in each hand, engaged in an altercation with another unarmed individual,” Norman said. They only fired after the armed man ignored multiple commands and moved toward the unarmed man, the chief said.

“This is a situation where somebody's life was in immediate danger,” Norman said.

The officers were wearing body cameras and the footage will be released per the policy of their department, Norman said.

The Columbus Police Department has received attention because of its special unit deployed to Milwaukee that works to improve police-community relationships and had a visible role in guiding the largely uneventful protests on Monday.

The shooting happened near King Park, roughly a mile from the convention centre, where a small group of protesters gathered before marching on Monday. That demonstration was followed by dozens of Columbus police officers, wearing blue vests that read: “Columbus Police Dialogue.”

The Milwaukee County Medical Examiner's Office said an autopsy was scheduled for Wednesday.