A gunman dressed in police uniform opened fire at a youth camp of Norway's ruling political party on Friday, killing at least 80 people, hours after a bomb killed seven in the government district in the capital Oslo.
Witnesses said the gunman, identified by police as a 32-year-old Norwegian, moved across the small, wooded Utoeya holiday island firing at random as young people scattered in fear. Norwegian television TV2 said the gunman detained by police was described as tall and blond and had links to right-wing extremism.
"We had all gathered in the main house to talk about what had happened in Oslo. Suddenly we heard shots. First we thought it was nonsense. Then everyone started running," a survivor, 16-year-old called Hana told Norway's Aftenposten.
"I saw a policeman stand there with earplugs. He said 'I'd like to gather everyone'. Then he ran in and started shooting at people. We ran down towards the beach and began to swim." Hana said the gunman fired at people in the water.
Many sought shelter in buildings as shots echoed across the island, ran into the woods or tried to swim to safety. Boats searched for survivors into the night, searchlights sweeping the coast. Rescue helicopters flew overhead.
The bomb, which shook the city centre in mid-afternoon, blew out the windows of the prime minister's building and damaged the finance and oil ministry buildings. Prime Minister Jens Stoltenberg, who was not in the building at the time, will give a press conference at 6am GMT on Saturday.
Explosives found on island
There were no immediate reports of other suspects. But acting police chief Sveinung Sponheim said authorities were working on the hypothesis that several people may have been involved.
Police seized the gunman, named by local media as Anders Behring Breivik, and later found undetonated explosives on the island, a pine-clad strip of land about 500m long, to the north-west of Oslo.
Breivik's alleged Facebook page (PDF) appeared to have been blocked by late evening. It had listed interests including bodybuilding, conservative politics and freemasonry.
Norwegian media said he had set up a Twitter account a few days ago and posted a single message on July 17 saying: "One person with a belief is equal to the force of 100 000 who have only interests."
About 10 police officers were outside the address registered to his name in a four-storey red brick building in west Oslo.
The Norwegian daily Verdens Gang quoted a friend as saying he became a right-wing extremist in his late 20s. It said he expressed strong nationalistic views in online debates and had been a strong opponent of the idea that people of different cultural backgrounds can live alongside each other.
With police advising people to evacuate central Oslo, and some soldiers taking up positions on the streets, the usually sleepy capital was gripped by fear of fresh attacks. Streets were strewn with shattered masonry, glass and twisted steel.
Norwegians reacted with horror to television images of the bodies of young men and women strewn around the island.
"I just saw people jumping into the water, about 50 people swimming towards the shore. People were crying, shaking, they were terrified," said Anita Lien (42) who lives by Tyrifjord lake, a few hundred metres from Utoeya island, north-west of Oslo.
"They were so young, between 14 and 19 years old."
A young girl, her hair still wet after escaping told TV2:
"He walked slowly but surely around it [the island] and shot everyone. Eventually he came to where I sat and then he slowly went over and shot ten people." She escaped by jumping into the water."
"He was so calm, that is what was so strange."
It is the most violent event to strike Norway since World War II," said Geir Bekkevold, an opposition parliamentarian for the Christian Peoples Party.
The prime minister declined to speculate on who had been involved. But he told a televised news conference. "No one will bomb us to silence, no one will shoot us to silence."