At least 12 people, including a police sergeant, were killed after a gunman opened fire on a crowd of mostly college students in a crowded country music bar in the suburb of Thousand Oaks, Los Angeles on Wednesday (Nov 7) night.

The shooting began at 23:20 local time about 40 miles (65km) north-west of Los Angeles, reported BBC citing police officials.

At least 200 people were reportedly inside the Borderline Bar and Grill, which was hosting a university student night, at the time of the attack.

Police have named the suspect as 28-year-old Ian David Long, who had suspected mental health issues.

Officials believe the US Marine Corps veteran and local resident took his own life inside the bar.

Ventura County Sheriff Geoff Dean named the suspect, who was also killed, as Ian Long, aged 28. Dean told a news conference Long had likely shot himself.

He said he appeared to have shot at random, using only a Glock .45-caliber handgun. There was no known motive.

It was the third mass shooting in the United States in under two weeks, six days after the death of two women at a yoga class in Tallahassee, Florida and 12 days after a gunman killed 11 worshippers at a synagogue in Pittsburgh.