Protests have grown in the United States 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 US 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.

WATCH: Do black lives matter in the US?

Sandra Augustus, an aunt who helped to 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.

Warning: This video contains scenes some readers may find distressing

 

'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 outside which Sterling worked, Abdul Muflahi, told local TV that the first officer to arrive at the scene had used a stun gun on Sterling and the second officer tackled the man. As Sterling fought to get the officer off 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 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 Attorney's 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 1 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.

Mobile phone footage

Footage of the moment Sterling was killed, which cannot be verified by Al Jazeera, contains images some readers may find distressing.

The 48-second video shows two police officers pushing Sterling down to the ground. One officer is seen pressing his head against the ground. There are shouts of "Get on the f*****g ground!" and "If you move, I swear to f*****g God!". Then, at least five shots can be heard. 

Seconds after the gunshots end, as blood pours from Sterling's ailing body, an officer can be heard saying "F***!" and, speaking into a radio, "Shots fired! Shots fired!".

Alton Sterling, 37, was a father of five and used to sell CDs outside the Triple Mart store in Baton Rouge [Reuters]

Reports said Sterling died minutes later, as paramedics arrived on the scene.

An autopsy showed that Sterling died of multiple gunshot wounds to the chest and back, according to East Baton Rouge Parish Coroner Dr William Clark.

Edwards, the Louisiana governor, announced that the US Justice Department investigation would be carried out by the department's civil rights division. Edwards said the video of Sterling's death is "disturbing, to say the least".

The Justice Department's investigation will look into whether the officers willfully violated Alton Sterling's civil rights through the use of unreasonable or excessive force.

Here is how some on social media have reacted to the killing of Alton Sterling:

 

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A photo posted by champagnepapi (@champagnepapi) onJul 6, 2016 at 5:50pm PDT

Source: Al Jazeera and agencies