A loud explosion shattered windows at the government headquarters in Oslo on Friday, injuring several people.
Norway's public broadcaster NRK says one person has been confirmed killed in the explosion at the government headquarters in Oslo and news agency NTB said police confirmed a bomb caused the explosion.
The buildings include the office of Norway's Prime Minister Jens Stoltenberg, who is safe, government spokeswoman Camilla Ryste told The Associated Press.
Witness Ole Tommy Pedersen was standing at a bus stop about 100 yards from the building at around 3.30pm (1430BST) when he saw the blast shatter almost all windows of the 20-floor building. He said a cloud of smoke is billowing from the bottom floors.
"I saw three or four injured people being carried out of the building a few minutes later," Mr Pedersen told The Associated Press.
Nearby offices were evacuated including those housing some of Norway's leading newspapers and news agency NTB.
An AP reporter at the scene saw one person with a bleeding leg being led away from the area.
Video shown by Norwegian broadcaster NRK showed most of the windows of the building had been blown out.
The bottom floor appeared to be completely gutted. Shattered glass and debris littered a square in front of the building. Nearby offices were evacuated including those housing some of Norway's leading newspapers and news agency NTB. Some of them were also damaged.
The government building houses the prime minister's office and his administration. Several ministries are in surrounding buildings.