"Five persons are confirmed shot," police said in a statement, adding that the extent of any injuries was unclear.
"This is currently seen as attempted murder, arson and aggravated weapons offence," the police said.
Ambulances, rescue services and police are onsite, a spokesperson for local rescue services said.
The shooting took place in a campus area where several schools, for both children and adults are located.
Police said students were held indoors at the affected school and also at nearby schools.
"The news of an attack at Orebro is very serious," Justice Minister Gunnar Strommer told public broadcaster SVT, adding that the government was in close contact with police.
