Just completely horrible. From The Guardian:
The detonation took place near the 17-storey government building where the prime minister has his offices and the headquarters of Norway’s biggest tabloid paper, VG. Witnesses said tables in the paper’s basement cafeteria were smeared with blood and scattered with glass and other debris. Residents were told to stay away from the town centre, or stay in their homes and hotel rooms.
In what Norwegian police said was a co-ordinated attack, about 700 youth members of the Labour party, some as young as 15, who were holding their annual summer camp on an island of Utoya, a lake west of Oslo, came under fire by a man dressed as a policeman armed with an automatic weapon. According to tweets by people at the event, some children escaped by climbing trees, hiding in the bushes or swimming away from the island. One party youth member tweeted: “We are sitting down by the beach. A man is shooting clothed in a police uniform. Help us! When are the police coming to help us!”
Counter-terrorist police flew to the island and it was reported that a man, described in reports as tall and blond, had been arrested.
The Guardian also has a live blog on the Oslo attacks here.