A teenager reportedly wielding a knife was arrested on Thursday after entering a school in southern Sweden and attacking an employee who was taken to hospital, police said.

Witnesses said the assailant walked through school wielding a large knife and wearing a helmet, a mask and what appeared to be a bullet proof vest, according to reports in local media.

Police arrived at the scene in the southern town of Eslöv after receiving an emergency call at 8.40am as the school day was getting under way.

“Police were able to overpower the suspect (…) it was quite chaotic at the scene,” police spokeswoman Ewa-Gun Westford told reporters.

They did not say whether the assailant, who is 15, was carrying a knife, confirming only that he had a weapon.

Swedish media reported that the boy was a student at the school.

He was arrested on suspicion of “attempted murder”, police said.

The 45-year-old school employee who was injured in the attack was taken to hospital for surgery.

Details of his injuries were not disclosed, but public broadcaster SVT reported on Friday that the man was awake and in stable condition.

Media reports said students were locked in their classrooms for more than 90 minutes during the incident, which took place on the second day of the school term.

Some students reportedly jumped out of classroom windows during the attack, witnesses told local media.

“There was a guy with a long knife who came into the school. He was wearing a mask with a skeleton on it, a helmet and what looked like a bulletproof vest. It was really scary,” one student told the regional Skånska Dagbladet newspaper.

Eslöv municipality said no students had been injured, and that pupils were later evacuated from the school to an adjacent sports hall.

“This is horrible. School should be a safe place for students, teachers and everyone who is there,” Eslöv mayor Johan Andersson said in a statement.

School attacks are rare in Sweden.

In October 2015, three people were killed in a racially-motivated attack at a school in the western town of Trollhättan by a far-right assailant later killed by police.