Police in Oslo say at least 80 people were killed in a horrific shooting at a youth camp near the Norwegian capital on Friday by the same homegrown terrorist who hours earlier set off a bomb in the city's government quarter, killing seven.

Police originally said nine or 10 people were killed at the camp, though eyewitness accounts put the death toll much higher.

Police director Oystein Maeland told reporters shortly after midnight, local time, they had discovered many more victims.

"It's taken time to search the area. What we know now is that we can say that there are at least 80 killed at Utoya," Maeland said. "It goes without saying that this gives dimensions to this incident that are exceptional."

Police say the Norwegian man linked to both attacks appears to have acted alone.

"It seems like that this is not linked to any international terrorist organizations at all," said one official, speaking on condition of anonymity. "This seems like a madman's work."

The attacks sent shockwaves across the country which on average year sees just 40 murders per year. It is said to be the deadliest bombing in Norway since the Second World War.

Shortly after the government quarter was rocked by the bombing on Friday, a gunman dressed as a police officer opened fire on Utoya, an island just outside the capital, where the youth wing of the ruling Labor Party was holding an event for hundreds of youths.

He was arrested shortly after the shooting and later linked to the bombing in Oslo. Police have since raided the suspect's Oslo apartment. The police have not released his name.

However, Norwegian media have identified the arrested man as 32-year-old Anders Behring Breivik.

On his Facebook page Breivik describes himself as a conservative Christian and indicates an interest in politics -- in particular with Winston Churchill and Max Manus, the noted Norwegian resistance fighter of the Second World War. As recently as a few days ago he was also posting various music videos.

Breivik appears to have lost or changed his job in 2008. Tax records posted online say his income dropped by half that year and show no income for 2009. On Facebook he describes himself as director of Breivik Geofarm.

Norwegian media reports describe Breivik as a right-wing extremist opposed to both Islam and multi-culturalism, and speculate that his farming business would have access to fertilizer that could be used to construct explosives.

His one and only Twitter entry, from July 17, reads "One person with a belief is equal to the force of 100 000 who have only interests" -- paraphrasing the English philosopher John Stuart Mill.

Speaking to CTV News Channel, security expert Alan Bell described Friday's events as an apparent "lone wolf domestic attack" similar to the Oklahoma City bombing.

"This is very similar," to the attack carried out by domestic terrorist Timothy McVeigh in 1995, said Bell, noting that the Oslo suspect, "obviously has a problem with either the political party or the prime minister and decided to take on the government himself -- and his way was to destroy things and kill people."

Police say the suspect was seen in Oslo before the explosion there, which killed seven, and that undetonated explosives were found on the island.

A number of camp attendees swam for their lives when the shooting broke out according to Norway's NRK network, prompting calls via Twitter and other social media for locals with watercraft to come to their rescue.

Resident André Skeie sped to the scene upon hearing of the shooting and took between 15 and 20 injured youths from the island.

"Several of them had gunshot wounds to the abdomen. The boat is full of blood," he told NRK. As many as 700 people were at the camp and Prime Minister Jens Stoltenberg had been due to attend.

A 15-year-old camper named Elise said she heard gunshots, but then saw a police officer and thought she was safe. Then he started shooting people right before her eyes.

"I saw many dead people," said Elise, whose father, Vidar Myhre, didn't want her to disclose her last name. "He first shot people on the island. Afterward he started shooting people in the water."

Elise said she hid behind the same rock that the killer was standing on. "I could hear his breathing from the top of the rock," she said.

The motive remains unknown, but both attacks were in areas connected to the ruling Labor Party government. The youth camp is organized by the party's youth wing, and prime minister had been scheduled to speak there Saturday.

Meanwhile, the bomb blast earlier in the day in the downtown core shattered windows and gutted the main floor of a key government building. Seven were killed in the blast, four of which have been identified, and nine or 10 were seriously injured say officials.

The bomb appears to have targeted the prime minister's office. But Stoltenberg was not among those injured; he was working at home and not in the building.

Stoltenberg urged Norwegians to not cave in to fear caused by the attacks, telling NRK: "It's frightening. That's not how we want things in our country. But it's important that we don't let ourselves be scared. Because the purpose of that kind of violence is to create fear."

The blast left glass, paper and debris everywhere. Most of the windows in the 20-floor high-rise building were blown out, while the bottom floor appeared destroyed.

Nearby buildings were also damaged and evacuated. Some of the buildings housed Norway's leading newspapers and NTB. The website of the NRK network showed images of a blackened car lying on its side amid the debris.

Ingunn Anderson, who works for NRK, says she was having a coffee with a colleague at downtown café when they heard the blast.

"All of a sudden, the building started shaking like crazy and we're hearing this big explosion," she told CTV News Channel from Oslo.

"We ran out into the street and saw a lot of chaos, with glass everywhere and people sitting with bandages, bleeding. There was a smell in the air like fire, smoke and fire."

The bombing was unusual for Norway. The country has been the target of threats over its involvement in conflicts in Afghanistan and Libya. But with several dead, this is thought to be the deadliest bombing in Oslo since the Second World War.

Prime Minister Stephen Harper said he was "shocked and intensely saddened," and that Canada stands with Norway in the wake of the attacks.

U.S. President Barack Obama said the attack is a reminder that the world has a role in stopping such terror from happening. He also expressed his condolences to Norway's people.

Oslo is known for the Nobel Peace Prize that is awarded there, which Obama received in 2009.

With reports from The Associated Press