Three people were killed and another was hospitalized after a helicopter crashed and caught fire Tuesday evening in the Chatsworth neighborhood of Los Angeles, US, according to the Los Angeles Fire Department (LAFD).

"Four patients have been assessed. Three patients have been determined deceased on scene. One patient has been transported to a local hospital in unknown condition," the department said in a statement.

The National Transportation Safety Board (NTSB) and the Federal Aviation Administration (FAA) will be handling the investigation, it added.

Earlier, local media reported that the helicopter, which belongs to NBC Los Angeles (KNBC-TV), was covering the scene of a major bus crash that left at least two people dead when it went down.

Captain Branden Silverman from the LAFD told reporters he did not want to speculate that it was a news helicopter "because we have not confirmed that yet."

The Los Angeles Police Department (LAPD) confirmed that the helicopter was not one of theirs.

Karen Bass, Los Angeles mayor, said she was "absolutely devastated" by the loss of life in Chatsworth.

"My heart is with the families and loved ones of those we lost in the tragic bus collision and helicopter crash," Bass said in US social media post.

Later, the mayor said she is on scene in Chatsworth receiving updates from LAFD and the public safety officials.

"I’m grateful to the first responders working through an incredibly difficult situation tonight. My thoughts are with everyone impacted by these tragedies, including the entire NBC4 family." (AA)