The mother of a black man shot repeatedly in the back by Wisconsin police called Tuesday for calm after two nights of violent protests, as her lawyer said it would take a "miracle" for her son to walk again.

"We really just need prayers," Julia Jackson said of her son Jacob Blake, seen in video being shot up to seven times at point-blank range by a white Kenosha, Wisconsin police officer as he tried to get into his car with his three children inside on Sunday.

With hundreds of protesters marching for a third night Tuesday and at least one small group of mainly white, heavily armed men vowing to protect property her call for healing took on greater urgency.

Clashes between a smaller group of demonstrators and police broke out later Tuesday, with protesters shooting fireworks at law enforcement officers who responded with rubber bullets, one of which hit AFP's reporter.

The most recent police shooting of an African American has sparked outrage and protests in US cities, including New York and Minneapolis.

The majority have demonstrated peacefully, though some protesters also burned cars and buildings on Sunday and Monday nights in Kenosha.

Jackson was visibly emotional as she urged peace ahead of a national protest planned for Washington this weekend, where Blake's shooting, the killing of George Floyd three months ago and other deaths have mobilized the powerful Black Lives Matter movement.

The damage caused on previous nights "doesn't reflect my son or my family," she said.

Then she issued a powerful call for unity and denunciation of racism in America.

"Clearly you can see by now that I have beautiful brown skin. But take a look at your hand. And whatever shade it is, it is beautiful as well," she said.

"God did not make one type of tree, or flower, or fish, or horse or grass or rock. How dare you ask Him to make one type of human that looks just like you?"

Lawyers for the family said one of the policeman's bullets shattered Blake's spine, and others damaged his stomach, colon, liver and arm.

Civil rights attorney Benjamin Crump said Blake was paralyzed.

"It is going to take a miracle for Jacob Blake Jr to ever walk again, he said."

- 'Attempted murder' -

Blake's mother said she was praying for the police. But his father, Jacob Sr, accused law enforcement who remain quiet about the incident of "senseless attempted murder."

"They shot my son seven times, like he didn't matter," Blake said, struggling to hold back tears. "But my son matters. He's a human being."

Jacob Blake's sister Letetra Widman added: "I'm not sad. I don't want your pity. I want change."

Blake, 29, was shot after trying to break up a domestic dispute, according to Crump.

A bystander video shows a police officer shooting seven times at Blake while tugging on his shirt as he tried to get into the car.

The children, Crump predicted, would have "psychological problems for the rest of their life."

One, aged eight, had been celebrating his birthday, Crump continued, adding: "Can you imagine what... (he) is going to think about every time he has a birthday?"

Officials say police had been called to a domestic disturbance but have not said why the two officers had their guns pulled.

Crump, who represents the families of Floyd and other black people unjustifiably shot and killed, demanded the two officers involved currently suspended be fired and charged.

"For black America, this is our reality," he said.

He pointed to another shooting last week.

Police in Lafayette, Louisiana are being accused of excessive force after firing nearly a dozen rounds into Trayford Pellerin, 31, who was carrying a knife and walking towards a convenience store on August 21.

- 'Sickened' -

Expecting another night of demonstrations, on Tuesday Kenosha authorities installed a temporary iron fence in front of the county courthouse, a scene of confrontations between police and protesters the last two nights.

Few police were seen in the city's streets, however. Later, as scuffles with demonstrators kicked off, law enforcement moved armored vehicles in front of the courthouse.

Meanwhile, Wisconsin governor Tony Evers urged protestors to remain peaceful as he called up more national guard troops ahead of an expected third night of protests.

"We cannot allow the cycle of systemic racism and injustice to continue," he said in a statement.

"We also cannot continue going down this path of damage and destruction."

In one parking lot, a small group of mainly white armed men calling themselves the "Armed Citizens To Protect Our Lives And Property" said they were there to protect buildings from more damage.

Former Kenosha alderman Kevin Mathewson, with a handgun on his hip and an AR-15 assault rifle strapped across his body, said the shooting of Blake "sickened" him but that he wanted to defend his community.

"Some do not realize by burning a building you are risking the lives of first responders and anyone who may be inside," he said, adding that he was armed to protect himself from others with guns.