The press official could not say how many people were killed or injured, but said a suspect had been arrested and the situation was under control.
The suspected attacker was using a bow and arrow, according to a Kongsberg police spokesman.
Police were first notified of the suspect at 18:15 local time, the spokesman also said. He said the suspect attacked people at several places before being arrested.
Asked whether the situation was being treated as terrorism, the police press officer said it was “not clear yet, it is too early to tell.”
Kongsberg is located 85 kilometers west of the capital Oslo.