A loud explosion shattered windows Friday at the government headquarters in Oslo which includes the prime minister's office, injuring several people.
Witness Ole Tommy Pedersen was standing at a bus stop about 100 meters (yards) from the high-rise at around 3:30 p.m. (1330 GMT) when he saw the blast shatter almost all windows of the 20-floor highrise. 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," Pedersen told The Associated Press.
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.
An AP reporter who was in the NTB office said the building shook from the blast and all employees evacuated the building as the alarm went off. Down at the street he saw one person with a bleeding leg being led away from the area.
The government building houses the prime minister's office and his administration. Several ministries are in surrounding buildings.
The blast comes as the Scandinavian country has grappled with a series of homegrown terror plots linked to al-Qaida, and six years after an uproar over cartoons of the Prophet Muhammad in neighboring Denmark.
Last week, a Norwegian prosecutor filed terror charges against an Iraqi-born cleric for threatening Norwegian politicians with death if he's deported from the Nordic country.
Danish authorities say they have foiled several terror plots linked to the 2005 newspaper cartoons of the Prophet Muhammad that triggered protests in Muslim countries.
Last month, a Danish appeals court on Wednesday sentenced a Somali man to 10 years in prison for breaking into the home of a cartoonist who caricatured the Prophet Muhammad.