Twin shooting and bomb attacks in Oslo and a nearby island have claimed at least 80 lives, a Norwegian police spokesman told AFP on Saturday.

"We have confirmation that at least 80 people are dead. We do not exclude a higher toll," said Are Frykholm.

Earlier reports said at least 10 people died when a Norwegian gunman disguised as a policeman opened fire at a youth camp meeting on an island outside the capital while seven perished in a bombing in central Oslo.

The bombing in the heart of the capital, where the prime minister's office and several government buildings are located, also left nine people critically injured.

The gunman has been identified as a 32-year-old Norwegian. According to the TV2 channel, he has links to right-wing extremists and possessed two weapons registered in his name.