A student opened fire at a high school outside Bangkok on Friday, killing at least six people and injuring several others, police said.

The attack took place at Debsirin Nonthaburi School in Nonthaburi province, northwest of the Thai capital, Royal Thai Police spokesperson Trairong Piwpan told The Associated Press (AP).

One witness said students barricaded themselves inside a classroom after hearing gunfire from another building. They remained there until police officers arrived, knocked on the door and escorted them safely out of the school.

About an hour after the shooting, people stood outside the school comforting one another while police officers and first responders moved through the campus.

Authorities gave conflicting accounts of the casualties that could not immediately be reconciled.

Trairong told broadcaster Channel 3 that the shooter was hospitalized in serious condition and that 15 other people were injured, including two who were in critical condition.

He said three teachers and three students were killed.

Health Minister Pattana Promphat said 22 people were injured, including nine in critical condition. Some were hurt in falls or other incidents during the chaos, and it was not immediately clear how many had been shot.

Deputy Interior Minister Polapee Suwunchwee told reporters at the scene that five teachers were killed and that the shooter had killed his two grandparents at home before going to the school. He also said the shooter later died at a hospital.

Trairong said investigators were still trying to determine a motive. He said the gun was believed to have been taken from a member of the student's family.

Prime Minister Anutin Charnvirakul offered his condolences and said he had ordered relevant officials to provide assistance to the victims.

In February, a 17-year-old stole a gun from a police officer and opened fire at a public high school in southern Thailand, briefly taking people hostage during a two-hour attack that killed one person and injured two others.

In 2023, a 14-year-old boy was accused of carrying out a shooting at a major shopping mall in Bangkok.