Network Seven cameraman Tim Myers was hit with a riot shield and punched in the face, while reporter Amelia Brace was clubbed with a truncheon.

Both were shot with rubber bullets and struggled to breathe after tear gas was thrown at the crowd.

Prime Minister Scott Morrison described the attack as troubling and has asked for an investigation.

Morrison has spoken to Seven to check on the crew’s welfare and offer his government’s support, should they wish to pursue a formal complaint against police through the Australian embassy.

He also ordered the embassy to investigate the incident and register Australia’s “strong concerns” with local authorities.

Federal Opposition Leader Anthony Albanese is concerned the pair were attacked by police while doing their jobs.

“In a democratic society the role of the media is critical, and it’s important the media are able to report on events, including crises such as we’re seeing in the United States, free from harassment,” he told reporters.

“The violence that has occurred towards members of the media is completely unacceptable.”

Cabinet minister Greg Hunt said the federal government was always concerned about the wellbeing of Australians overseas.

“The Department of Foreign Affairs and Trade is intensely focused on the safety and welfare of Australians,” he told reporters.

A Nine Network crew was detained and searched by Minneapolis Police on Monday.

Reporter Tim Arvier said his cameraman and security guard were handcuffed but the officers were respectful and soon let the Australian crew go.

The Media, Entertainment and Arts Alliance has written to the US ambassador in Canberra to protest the attacks on journalists covering the civil unrest.

The moment our @7NewsAustralia team is attacked by police. Cameraman Tim Myers has covered war zones around the world. Today this is what confronted him and @AmeliaBrace outside the White House pic.twitter.com/KPY0NZIwsm

— Ashlee Mullany (@AshleeMullany) June 1, 2020

Demonstrators were attacked by police near the White House as US President Donald Trump vowed a massive show of force to end violent protests over the death of a black man in police custody.

Law enforcement, including officers on horseback, moved on protesters in Lafayette Park, across the street from the White House as Trump made his remarks from the Rose Garden on Monday.

The president pledged to end six nights of looting and violence in major cities across the nation “now”, saying that he would deploy the military if state governors refused to call out the National Guard.

“Mayors and governors must establish an overwhelming law enforcement presence until the violence has been quelled,” Trump said in remarks at the White House Rose Garden as authorities dispersed protesters with tear gas just blocks away.

“If a city or state refuses to take the actions that are necessary to defend the life and property of their residents, then I will deploy the United States military and quickly solve the problem for them,” he said.

“We are ending the riots and lawlessness that has spread throughout our county. We will end it now.”

Following his brief address in the Rose Garden, Trump walked out of the White House grounds and toward St. John’s Church, which was damaged in the protests on Sunday.

The president held a Bible as he stood in front of the boarded up church building in Lafayette Square, just north of the White House.

“We have the greatest country in the world,” the president said outside the church.

The demonstrations, which have been largely peaceful but have turned violent after dark, have erupted across the country over the death of George Floyd, a 46-year-old who died in Minneapolis police custody after being pinned beneath a white officer’s knee for nearly nine minutes.

Floyd repeatedly said that he couldn’t breathe.

The officer has since been fired and been charged with third-degree murder and second-degree manslaughter, but protests have spread across the nation.

A senior US defence official, who spoke on condition of anonymity, said all of the 1200 National Guard forces in Washington DC, had been mobilised and five states were sending 600 to 800 additional Guard troops who could be on the ground by evening.

A second defence official said some of the Guard troops were armed with lethal weapons.

Beyond that, active US military duty troops – including military police and engineering units – were on standby in the National Capital Region but outside the city itself and were ready to deploy if needed.

The hope, the first official said, was that the additional Guard units would make the use of active duty troops unnecessary.

“A decision to put active-duty troops on the streets would have to be made by the president at this point,” the official said.

US Defense Secretary Mark Esper, Army General Mark Milley, chairman of the Joint Chiefs of Staff, Attorney General William Barr and others would be at a Department of Justice to coordinate the response, the first official said.

Two doctors who carried out an independent autopsy of say the cause of Floyd’s death was “mechanical asphyxia” and that his death was a homicide.

The doctors on Monday also said Floyd had no underlying medical conditions that contributed to his death – and that he was likely dead before he was placed into an ambulance.

That contradicts the initial findings of the official autopsy by the Hennepin County Medical Examiner, which was cited in the court charging document against the police officer who drove his knee into Floyd’s neck for several minutes.

Those initial findings said there was no evidence of traumatic strangulation. It also said coronary artery disease and hypertension also likely contributed to Floyd’s death.

The county’s full autopsy report has not yet been released. Later on Monday, the medical examiner declared Floyd’s death was a homicide.

“The evidence is consistent with mechanical asphyxia as cause of death and homicide as manner of death,” said Dr. Allecia Wilson of the University of Michigan, one of the two forensic doctors who performed an independent autopsy.

Dr. Michael Baden, who also took part in the independent autopsy at the behest of Floyd’s family, said that two other police officers who pressed their knees into Floyd’s back also caused him to stop breathing.

“We can see after a little bit less than four minutes that Mr. Floyd is motionless, lifeless,” Baden said, adding he found no underlying health conditions in Floyd that caused his death.

Dozens of cities across the United States remain under curfews at a level not seen since riots following the 1968 assassination of civil rights activist Martin Luther King Jr.

The National Guard deployed in 23 states and Washington DC.

Curfews were extended in Washington DC, where authorities fought to put out fires near the White House overnight; in Minnesota, which has experienced some of the worst violence, and in Los Angeles.

One person was killed in Louisville, Kentucky, overnight where police and National Guard troops returned fire while trying to disperse a crowd.

Police in Chicago, the country’s third-largest city, fielded more than 10,000 calls for looting, Mayor Lori Lightfoot told a briefing.

On Monday, dozens of people quietly paid their respects to Floyd at the scene outside the Cup Foods where he lost his life. Visitors left flowers and signs honoring Floyd on the pavement.

Terrence Floyd, the victim’s brother, told the gathering he wanted people to get educated, vote and not destroy their own communities.

“Let’s do this another way,” he said.

-with AAP