Three police officers dead, seven critical after US shooting

Video footage broadcast on television showed police responding to the scene in Baton Rouge as multiple shots forced civilians to back away in cars.

"They are in extremely bad shape," WAFB television reported of the officers.

No motive was reported for the attack, however an escalating tension has ripped through the US in recent weeks after several incidents.

Earlier this month, officers shot dead a man after he targeted and killed five officers and injured seven others during a demonstration against the murder of two black men at the hands of police.

Gunfire broke out as hundreds of people were peacefully gathered to protest fatal police shootings in Louisiana and Minnesota, causing scenes of chaos.

The deaths of Alton Sterling in Louisiana and Philando Castile in Minnesota are once again fuelling debate about police use of lethal force, especially against blacks.

Castile's girlfriend Diamond Reynolds live-streamed the aftermath of Wednesday night's shooting in a Saint Paul suburb with an officer pointing his gun at her through the window as her four-year-old daughter sat in the back of the car.

The 10-minute video – which shows Castile bleeding profusely – prompted widespread outrage and has been viewed millions of times after it was posted on Facebook.

It prompted thousands to march across Los Angeles, Chicago, Washington, Dallas and Atlanta on Thursday evening, with more than 1,000 protesters gathered in New York's Time Square.

The Dallas ambush marked the single biggest loss of life for law enforcement in the United States since the September 11, 2001 terror attacks.