Anyone in the area that could shed some light?
"We're not sure it's just one person... based on statements from witnesses, we think there may be more," Acting Police Chief Sveinung Sponheim said.
A 32-year-old Norwegian was arrested and charged with terrorism, but police have not officially released his name. Local media has identified the man as Anders Behring Breivik, who has been described as a right-wing Christian fundamentalist.
At least 85 others were killed in a shooting at a youth camp in nearby Utoya island.
The man asked to address the group, and then started shooting. According to police, the gunman was active and shooting for an hour and a half before authorities arrived. He used at least one automatic weapon and one handgun, police said.