Media playback is unsupported on your device Media caption The BBC's Alastair Leithead: "Five shots were fired"

US police have shot and killed a homeless man during an altercation in central Los Angeles, in an incident caught on video.

The graphic film shows a violent struggle between the man and several officers in the city's Skid Row area.

Police say that three officers opened fire after the man tried to grab a gun from an officer.

Witnesses said the dead man was known as Africa and had been homeless after treatment for mental illness.

The LA police department said officers had been responding to reports of a robbery and had attempted to use a Taser to subdue the suspect but he had "continued fighting and resisting".

Media playback is unsupported on your device Media caption A witness said five officers were involved in the altercation

No other gun was recovered at the scene, LA police commander Andrew Smith said.

Last year, highly publicised killings of black men sparked weeks of protests in the US.

Hours after the latest shooting, the hashtag #LAPDShooting was trending on Twitter in the US.

LA police fatal incidents 16 People shot dead by police in city of Los Angeles in 2014 252 People killed by police in LA since 2000 606 People killed by police in LA county since 2000

38 People killed by police in LA county in 2014

Shooting victim

Nicknamed Africa, had been living on the street for months, eyewitnesses say

Said to have spent 10 years in a mental health institution before winding up homeless

Said by people who knew him to have not been violent but still exhibited "mental problems"

Sources: LA Times and ABC News

It is unclear from the video what exactly happened, the BBC's Alastair Leithead reports from Los Angeles.

The video begins with what appears to be a black man swinging punches at four police officers in daylight, near the tents and cardboard of a pavement homeless camp. Two other officers run up to join their colleagues.

Image copyright FACEBOOK/ANTHONY BLACKBURN Image caption The video posted on Facebook showed the altercation leading to the shooting

As the man is knocked to the ground, a woman can be seen picking up a fallen police baton and a voice seems to shout "Give me my stick! Give me my stick!"

Several police officers turn to tackle the woman, in the foreground of the video, and her detention partially obscures what is happening with the man on the ground.

A voice can be heard shouting "Drop the gun!" four times before five shots ring out.

The police officers step away from the suspect lying on the ground. No-one approaches the body again for one minute and 13 seconds, by which time police reinforcements have arrived.

The man taking the video can be heard swearing as he records it.

After the shooting, he can be heard saying. "Ain't nobody got no [obscenity] gun. I'm gonna record this [obscenity]... They just shot that man right here, man, they just shot that [obscenity] man right here, yeah."

Image copyright AFP Image caption The man was shot dead in Skid Row, where many of LA's homeless live

Skid Row

Name given to a central district of Los Angeles with a large homeless population

Estimates of district's population range from 8,000 to 11,000 people, predominantly black, with a homeless population of about 2,500, according to the LA Chamber of Commerce

Described by the Associated Press news agency as a "tenuous comfort zone for many who hit the rock bottom of their lives in America"

Homeless people tended to gravitate to the area historically as it was near a railway terminal - "the last stop on the train for the whole country", according to the Union Rescue Mission charity

Other US cities have their own "skid rows", with the term believed to have originated in Seattle, Washington state

Other cameras

Commander Smith said three officers, including a sergeant, had fired their guns as they struggled on the ground for control of one of the police officer's weapons.

He said the department was aware of the amateur video and would attempt to amplify its sound and pictures to establish exactly what had happened.

"The video is disturbing," he told reporters. "It's disturbing any time anyone loses their life. It's a tragedy."

The commander added that at least one of the police officers had been wearing a body camera.

According to an ABC News report, the three officers have been placed on leave pending the outcome of an investigation into the shooting.

Steve Soboroff, president of LA's Police Commission, told the BBC it was important to investigate the facts before making any conclusions.

Witnesses told the Los Angeles Times that the man who died had been living on the street for four or five months.

Ina Murphy, who lives in an apartment nearby, said he had told her that he had recently been released after spending 10 years in a mental health facility.

People on Skid Row who knew him said he was not violent.

"What did he do?" said Steven Tugmon to ABC News. "He wasn't an aggravated person. He wasn't mad all the time. He just had mental problems."