Protests grow in US over police killing of black man

Demonstrators mourned the loss of Alton Sterling, chanting "black lives matter" and "hands up don't shoot" [Bryn Stole/Reuters]

As probe into death of black father of five gathers pace, more footage emerges of moment he was killed by police.

Protests have grown in the US over the killing of Alton Sterling, a black man who was shot dead by white police in Louisiana, as an investigation into his death was announced.

Hundreds gathered in Baton Rouge on Wednesday night, a day after Sterling was wrestled to the ground by two officers and killed outside a shop as he sold CDs - an incident filmed with a mobile phone.

The rallies came as more mobile phone footage alleged to be of the incident emerged, and as the United States Justice Department said it would investigate the killing.

Many carried signs to express their anger and demand for justice, blocking streets near the shop where Sterling, a father of five, died.

Demonstrators chanted "black lives matter" and "hands up don't shoot".

Protesters and friends of Sterling had earlier erected a makeshift memorial on the white folding tables and fold-out chair he had used to sell mixtape CDs.

Sandra Augustus, an aunt who helped raise Sterling after his mother died, spoke to the crowds with a broken voice.

She said a second video that emerged on Wednesday showing the moments before her nephew was shot had left her angry.

She pleaded for protesters and those gathered not to allow the vigil to be marred by violence.

Shortly after speaking, Augustus and another aunt of Sterling's fainted in the heat and commotion. They were carried away by family members.

Louisiana Governor John Bel Edwards and the US Justice Department announced on Wednesday afternoon that there would be an investigation by the department's civil rights division.

'Man with a gun'

Baton Rouge police spokesman, L'Jean McKneely, told local media that officers had responded to an anonymous call that said there was a man in the area with a gun.

Louisiana is an "open carry state", meaning that with some exceptions adults can be armed if the gun is visible.

The owner of the shop outsied of which Sterling worked, Abdul Muflahi, told local TV that the first officer to arrive to the scene had used a stun gun on Sterling and the second officer tackled the man. As Sterling fought to get the officer off of him, the first officer shot him "four to six times".

In the footage circulated online five shots can be heard. 

The store owner said Sterling did not have a gun in his hand at the time, but he saw officers remove a gun from Sterling's pocket after the shooting.

A community vigil in memory of Alton Sterling was held and tributes poured from friends and family [Jeffrey Dubinsky/Reuters]

Baton Rouge Police Chief Carl Dabadie Jr. called Sterling's death a "horrible tragedy" and said there were still questions about what happened.

Quinyetta Mcmillon, the mother of Sterling's 15-year-old son addressed media, saying: "As a mother, I have now been forced to raise a son who is going to remember what happened to his father."

Community leaders said they did not trust the police and demanded answers.

The head of the National Association for the Advancement of Coloured People (NAACP) in Baton Rouge, Michael McCalahan, called for the police chief to be fired.

"We are going to turn the entire case over to the US Attorneys office and the FBI to conduct the investigation from this point," he said, shortly after the announcement.

"What we're going to do today is root out the one percent of bad police officers that go around becoming the judge, the jury and the executioner of innocent people. Period. But more specifically, innocent black lives," McCalahan said.