At least 10 people were killed and an unidentified number injured at a shooting at a school for adult education in central Sweden on Tuesday, the authorities said.

The police said they had started a “major operation” and locked down the campus in the city of Orebro, after shots were heard about 12:30 p.m. local time.

“This is an awful, exceptional incident — a nightmare,” said Roberto Eid Forest, head of the local police. “We do not think there is any terror motive behind this, but it is too early in the investigation to say,” Mr. Forest added on Tuesday evening.

“We think we have the perpetrator but we are not ruling out anything,” he said.

Images on Swedish news outlets earlier in the day showed dozens of police cars surrounding the school.