A 15-year-old student has opened fire at his Michigan high school, killing three students and wounding eight other people, including at least one teacher, authorities say.

Oakland County Undersheriff Mike McCabe said at a news conference that investigators were still trying to determine a motive for Tuesday’s shooting at Oxford High School in Oxford Township, a community 50 kilometres north of Detroit.

Mr McCabe said he was aware of allegations circulating on social media that there had been threats of a shooting at the roughly 1700-student school before Tuesday’s attack, but he cautioned against believing that narrative until investigators can look into it.

The vandalism prompted school administrators to post two letters to parents on the school’s website this month, saying they were responding to rumours of a threat against the school but had found none.

Authorities did not immediately release the suspect’s name, but Mr McCabe said deputies arrested him within minutes of arriving at the school in response to a flood of emergency calls about the attack, which happened shortly before 1pm.

He said the deputies also recovered the semi-automatic handgun and several magazines used to store ammunition that the suspect used in the attack.

“He fired multiple shots,” Mr McCabe said. “Somewhere in the area of 15 to 20.”

The three students who were killed were a 16-year-old boy and two girls, ages 14 and 17, Mr McCabe said. Two of the wounded underwent surgery and the six others who were wounded were in stable condition.

Mr McCabe said the suspect’s parents visited their son where he was being held and advised him not to talk to investigators, as is his right.

Police must seek permission from a juvenile suspect’s parents or guardian to speak with them, he said.

Oakland County Prosecutor Karen McDonald said her office expected to issue charges quickly.

Mr McCabe said he was not aware of any prior run-ins the suspect had with law enforcement or if he had any disciplinary history at school.

Governor Gretchen Whitmer also spoke at the news conference, saying, “I think this is every parent’s worst nightmare”, while choking up.

President Joe Biden, before delivering remarks at a community college in Rosemount, Minnesota, said: “As we learn the full details, my heart goes out to the families enduring the unimaginable grief of losing a loved one.”

The school was placed on lockdown after the attack, with some children sheltering in locked classrooms while officers searched the premises.

They were later taken to a nearby Meijer grocery store to be picked up by their parents.

Mr McCabe said investigators would pore over the school’s video footage and look through social media posts for any evidence of a possible motive.

A vigil was held at Lakepoint Community Church on Tuesday night.