KENOSHA (REUTERS) - Black Lives Matter organisers in Kenosha, Wisconsin, planned for a mass rally and march on Saturday (Aug 29) as reinforced National Guard units stood by with orders to prevent a resurgence of the unrest that convulsed the lakeside city earlier in the week.

A tense calm prevailed for a third night on Friday in the downtown area surrounding a courthouse and park that was the hub of tumultuous protests in support of Mr Jacob Blake Jr, the Black man shot in the back by a white police officer on Sunday.

The shooting of Mr Blake, in front of three of his children, turned the mostly white city of 100,000 people on Lake Michigan, 64km south of Milwaukee, into the latest flashpoint in a summer of nationwide demonstrations against police brutality and racism.

Mr Blake, 29, survived but was left badly wounded and paralysed from the waist down.

Anger at the shooting, captured on video that went viral, soon escalated into pitched street skirmishes, with protesters hurling firecrackers and bricks at police in riot gear who fired volleys of tear gas and rubber bullets.

Despite a dusk-to-dawn curfew, a wave of arson attacks and vandalism devastated a predominantly minority district on Monday night, and on Tuesday night three demonstrators were shot - two fatally - by a white teenager armed with a semi-automatic rifle.

The 17-year-old suspect, Kyle Rittenhouse, who walked away from the scene as police looked on, surrendered to law enforcement on Wednesday near his home in Illinois, not far from the Wisconsin border, according to his lawyers.

Since mid-week, as Governor Tony Evers deployed additional Wisconsin National Guard troops to help local law enforcement restore order, the unrest has subsided.

BOOTS ON THE GROUND

By Friday, more than 1,000 Guard soldiers were on the ground, many brought in from out of state, ahead of a large protest march through Kenosha planned by activists for Saturday afternoon.

In Illinois on Friday, a hearing on a bid by Kenosha prosecutors to extradite Rittenhouse back to Wisconsin was postponed while the teen, a former lifeguard jailed held without bond, arranged for a private legal team.

He has been charged with six criminal counts, including first-degree intentional homicide, attempted homicide, reckless endangerment and unlawful possession of a firearm by a minor.

One of his lawyers, prominent Atlanta-based trial attorney Lin Wood, said his client acted in self defence.

"An egregious miscarriage of justice occurring with respect to this 17-year-old boy," Mr Wood wrote on Twitter on Friday.

Mr Blake, who has undergone multiple surgeries since the shooting, had been handcuffed to a hospital bed because of an outstanding arrest warrant. The handcuffs were removed on Friday and officers guarding Blake stood down after the warrant was vacated, his attorney, Mr Pat Cafferty, told Reuters.

The warrant was based on a criminal complaint filed against Mr Blake in July based on statements made by his ex-girlfriend, the mother of three of his children, that was released to Reuters on Friday.

The woman told police Mr Blake broke into her home on May 3 and sexually assaulted her before stealing her truck and debit card.

Wisconsin Attorney General Josh Kaul said this week that police confronted Mr Blake when called to the home of a woman who had reported her "boyfriend was present" without permission, and officers tried to arrest him. Mr Kaul said efforts to subdue Mr Blake with a Taser failed, and that investigators later recovered a knife from the floor of the car that Mr Blake was leaning into when he was shot.

On Friday, the Kenosha police union defended the officers, saying Mr Blake was armed with a knife, fought the officers and was given several chances to cooperate before they used deadly force. This account, in a statement by union lawyer Brendan Matthews, said the scuffle with police included Mr Blake "putting one of the officers in a headlock."

Mr Blake's lead attorney, Mr Ben Crump, has said his client was not armed with a knife and did not provoke or threaten police.

Demonstrators and Mr Blake's family have demanded that the three officers involved in the encounter, including the policeman who shot all seven bullets at Mr Blake from behind at point-blank range, be fired and prosecuted.

The three have all been placed on administrative leave, pending an investigation by the Wisconsin Justice Department.