A massive bomb blast has hit government buildings in the Norwegian capital Oslo, killing at least two people and injuring 15 others.
PM Jens Stoltenberg described the situation as "very serious".
The bomb was followed by a shooting incident near Oslo at a youth meeting of the Labour Party, which Mr Stoltenberg leads.
Unconfirmed reports said a man dressed as a police officer had opened fire indiscriminately, injuring five.
No group has said they carried out the attacks.
Hours after the bomb struck Oslo, officials said some people were still inside the damaged buildings, some of which were on fire.
Television footage from the government quarter showed rubble and glass from shattered windows in the streets - smoke was rising from some buildings where fires were burning. The wreckage of at least one car was on one street.
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All roads into the city centre have been closed, said national broadcaster NRK, and security officials evacuated people from the area, fearing another blast.
Mr Stoltenberg, in a telephone call to Norwegian television, said all government ministers were believed to be safe.
He said he had been advised by police not to reveal his current location.
"Even if one is well prepared, it is always rather dramatic when something like this happens," he said.
Egil Vrekke, Assistant Chief Constable of Oslo police told the BBC the rescue operation was ongoing.
"We are issuing warnings just make sure people are not in the area in case there are further explosions," he told the BBC.
"We have cordoned off large areas. There are bomb experts at the scene investigating whether there are other devices in the area."
A spokesman for Oslo University hospital said seven people had been taken there for treatment.
'Focus on rescue'
Hours later, reports emerged of a shooting at a Labour Party youth camp in Utoeya, and island outside the capital.
Mr Stoltenberg, who had been due to visit the camp on Saturday, told TV2 the situation in Utoeya was critical.
At least 500 people were at the camp, said reports, and five people were said to have been injured.
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Assistant Chief Constable Egil Vrekke: "There are a lot of casualties"
State Secretary Kristian Amundsen said Friday was a public holiday in Norway so the government offices were not as busy as they might usually have been.
"But there are many hundreds of people in these buildings every day," he told the BBC.
"We have to focus on the rescue operation - there are still people in the building, there are still people in the hospital."
Reuters said the oil ministry was among the other government buildings hit.
Oistein Mjarum, head of communications for the Norwegian Red Cross, said his offices were close to the site of the explosion.
"There was a massive explosion which could be heard over the capital Oslo," he told the BBC.
"This is a very busy area on Friday afternoon and there was a lot of people in the streets, and many people working in these buildings that are now burning," he said.
An NRK journalist, Ingunn Andersen, said the headquarters of tabloid newspaper VG had also been damaged.
"I see that some windows of the VG building and the government headquarters have been broken. Some people covered with blood are lying in the street," AP quoted her as saying.
"It's complete chaos here. The windows are blown out in all the buildings close by."
Local resident Silvio told the BBC the blast shook everything in his apartment.
"I went running out onto the street to see what happened. All the neighbours came running out too."
He said he saw two or three unconscious people being carried on stretchers and others on the floor.
"If they were dead or not I wouldn't be able to tell you but they were receiving assistance at the time."
"The police were clearing the area and there was already various security guards who were going over to attend to the various shops whose glass had been broken out."
Mr Mjarum said people across the Oslo and Norway were in shock.
"We have never had a terrorist attack like this in Norway - if that's what it is - but of course this has been a great fear for all Norwegians when they have seen what has been happening around the world."
The United States has condemned the "despicable acts of violence" in Oslo, while the President of the European Council, Herman Van Rompuy, said he was "deeply shocked" by "these acts of cowardice for which there is no justification".