CHICAGO (REUTERS) - Chicago's police accountability office on Thursday (April 15) released to the public body-camera video footage showing a police officer shooting and killing a 13-year-old boy in an alley more than two weeks ago.

The nine-minute video began by showing an unidentified police officer getting out of his squad car and running after Adam Toledo in an alley at 2.30am on March 29 in Little Village, a neighbourhood on the city's West Side.

The video then showed the officer yelling "stop" to Adam before he caught up to him and ordered him to show him his hands. Adam appeared to raise his hands right before the officer fired one shot and then immediately ran to the boy as he fell to the ground.

"Shots fired, shots fired. Get an ambulance over here now," the officer is heard saying in the video.

The Chicago Police Department said immediately following the incident that Adam had a gun in his hand. It is unclear in the video whether he did at the time of the shooting.

Officers were chasing Adam and a man after they received notification of shots fired in the area, the department said.

"There were a number of forces that met up at 2.30 in the morning on March 29 in an alley, and, simply put, we failed Adam," Chicago Mayor Lori Lightfoot said during a news conference before the video was released.

The city's Civilian Office of Police Accountability also released third-party video and other materials related to the incident.

The incident, along with Sunday's fatal police shooting of Daunte Wright in a Minneapolis suburb and the murder trial of former Minneapolis police officer Derek Chauvin over the May 2020 death of Mr George Floyd, has raised tensions in Chicago.

"Chicago, as well as way too many parts of our country, has a long legacy of police violence and police misconduct that have left far too many residents, especially those who are black and brown, in a constant state of fear and pain," Ms Lightfoot said.

City officials urged people to remain calm as they prepared for civil unrest following the release of the video footage.

They said more police officers and city equipment would be in place to protect businesses during any unrest. Like some other American cities, Chicago experienced riots and looting after Mr Floyd's death, which was also caught on video.

Adam's family said in a statement released to local media that they appreciated the support they had received from the community and were grateful that protests in Chicago over the last few days remained peaceful.

"We pray that for the sake of our city, people remain peaceful to honour Adam's memory and work constructively to promote reform," the family said.

WARNING: The graphic content in this video may be disturbing to some.