The shooting is considered to be the deadliest school attack in the country's history.

"Around 10 people have been killed today," Orebro police chief Roberto Eid Forest told reporters.

The police could "not be more specific about the number due to a large number of wounded".

He provided no details about the number of wounded.

"This is a terrible event. This is exceptional, a nightmare," Forest said.

Police did not reveal any identity or ages of the dead, nor whether they were students or teachers at the Campus Risbergska secondary school for young adults.

Several media reported the suspected gunman turned his gun on himself but police would not confirm those reports.

"The suspected assailant is not known to police. He has no connection to any gang," Forest said, referring to the surge in deadly shootings and bombings linked to gang violence that have been on rise in Sweden in recent years.