At least a dozen deaths reported after a massive bomb blast hits central Oslo and a youth camp is fired upon.

Up to 17 people have been killed in two attacks in Norway: a bomb blast that went off near a government building housing the prime minister’s office in Oslo, followed by a shooting incident at a youth camp near the city.

The explosion in the Norwegian capital, which took place at 3:20pm local time, blew out most of the windows of a 17-storey building housing Jens Stoltenberg’s office in the city centre. It also damaged nearby ministries, including the finance and oil ministry, which was on fire.

The bomb killed at least seven people and left up to 15 others injured.

In the shooting incident, at a meeting organised by the ruling Labour party on Utoya island, nine or 10 people were killed and the suspected assailant – said to be a Norwegian man who was disguised as a police officer – was arrested, according to the AFP news agency.

A witness described the shooting in Utoya from his position, saying: “There is a little war going on out there.”

The attack on the youth camp happened two hours after the Oslo bomb blast. There was no immediate claim of responsibility for any of the attacks.

Anti-terrorism police were deployed to restore order, government officials said.

Prime minister unhurt

Stoltenberg was safe and was not in his office at the time, officials said.

The prime minister later appeared on Norwegian TV to say it was too early to call the Oslo blast a terror attack, although police confirmed it was a bomb.

They did not give further details.

“We do not know for sure what happened but it is a very serious explosion,” Stoltenberg said, adding those behind the attack wanted to spread fear.

Al Jazeera’s Jonah Hull described Oslo as a city “mostly shut down [and] extremely quiet”.

In Video Justin Crump, a security analyst, discusses the deadly attacks in Oslo and Utoya

“One gets the sense that it is really vastly changed in character [after the attacks],” he said.

“The bars are closed; the restaurants are closesd; not many people are about on what would have been a busy Friday.”

He said there were many unaswered questions “chief among them, of course, why Norway. Why this happened?”

Earlier, Peter Svaar, a local journalist, said “the whole of downtown Oslo is sealed off” and spoke of a “very chaotic situation”.

Hanne Taalsen, a journalist working for TV2, told Al Jazeera the blast caused “massive damage in the streets” around the government buildings.

The TV station’s building was later cordoned off amid reports that there was a suspicious package inside.

Newspaper offices in the area were also damaged and smoke could be seen drifting in the streets.

“People are really surprised. I am very surprised. People are shocked that this could happen in Oslo,” Taalsen told Al Jazeera.

“People are quite calm, they are not running around or anything. But people are quite shocked. I think most Norwegians consider themselves to be outside of incidents like this.”

The attack comes days after Norwegian prosecutors filed a terrorism charge against Mullah Krekar, founder of the Kurdish Islamist group Ansar al-Islam, who is accused of threatening a former minister, Erna Solberg, with death.

Norway has previously received threats from al-Qaeda over its involvement in combat operations in Afghanistan, where it has 406 troops.

It has also taken part in the NATO bombing of Libya, where Muammar Gaddafi, the Libyan leader, has threatened to strike back in Europe.