Many were also reported wounded from the bomb blast in central Oslo and the shooting at a summer school meeting of Prime Minister Jens Stoltenberg's ruling Labour Party outside the capital.
Authorities were reeling, with police saying they had no clue who or what was behind the attack, but media reported that the gunman behind the shooting had been arrested.
The United States and Europe immediately denounced the attacks and vowed solidarity with NATO member Norway -- an enthusiastic participant in international military missions that has forces in Afghanistan and is participating in Western air strikes in Libya.
Police said a "bomb" was behind a "powerful explosion" that tore through the government quarter in central Oslo, home to the prime minister's office, the finance ministry and some of the country's leading media.
Stoltenberg was safe and there were no reports of other senior government officials being killed or wounded. The government was to hold a crisis meeting later Friday.
"We can confirm that we have seven dead and two have been seriously injured" in the bomb attack, a police spokesman told reporters at a briefing in Oslo. Several dozen were also wounded, police said.
"We have no main theory, we don't even have a working theory," a police official said separately. "We already have enough to do to get an understanding of the situation." Police did say however, that they believed the two attacks were connected.