Police in the former auto manufacturing centre of 100,000 people midway between Milwaukee and Chicago said Blake was gunned down while they were responding to a call about a domestic dispute.
They did not immediately disclose the race of the three officers at the scene or say whether Blake was armed or why police opened fire, and they released no details on the domestic dispute.
A young man who said he made a widely seen cellphone video of the shooting, 22-year-old Raysean White, said that he saw Blake scuffling with three officers and heard them yell, "Drop the knife! Drop the knife!" before the gunfire erupted. He said he didn't see a knife in Barnes' hands.
The governor said he has seen no information to suggest that Blake had a knife or other weapon, "but this is undergoing a thorough investigation" by the state Justice Department.
The officers were placed on administrative leave, standard practice in a shooting by police, in the meantime.
Evers was quick to condemn the shooting, saying that while not all details were known, "what we know for certain is that he is not the first black man or person to have been shot or injured or mercilessly killed at the hands of individuals in law enforcement in our state or our country."
Democratic presidential nominee Joe Biden called for "an immediate, full and transparent investigation" and said the officers "must be held accountable."
"This morning, the nation wakes up yet again with grief and outrage that yet another Black American is a victim of excessive force," he said, just over two months before election day.
The United States is already roiled by the recent deaths of George Floyd in Minneapolis, Rayshard Brooks in Atlanta and Breonna Taylor in Louisville, Kentucky. "Those shots pierce the soul of our nation."
Republicans and the police union accused the politicians of rushing to judgment, reflecting the deep partisan divide in Wisconsin, a key presidential battleground state.
Wisconsin GOP members also decried the violent protests, echoing the law-and-order theme that US President Donald Trump has been using in his re-election campaign.
"As always, the video currently circulating does not capture all the intricacies of a highly dynamic incident," Pete Deates president of the Kenosha police union, said. He called the governor's statement "wholly irresponsible."
- AP
