The Norway massacre that killed 77 people on July 2011 was wholly preventable, a new commission report on the incident said on Monday, faulting the Norwegian authorities for their monumental lapses that allowed a lone assailant to maim and kill almost unhindered.

Gunman Anders Behring Breivik was able to bomb a government building located in the country's capital, Oslo, due the absence of security implements that were normally in place on important state facilities.

The report noted that earlier security plans of closing Oslo's government complex to vehicular traffic went unheeded until Mr Breivik parked his vehicle, which was packed with fertiliser bomb, on that fateful day of July 22 last year.

National security was so lax that the car bomb had successfully secured a parking spot metres away from the front office of Norwegian Prime Minister Jens Stoltenberg.

When Mr Breivik detonated his death cocktail, eight persons immediately perished and the country's chief political figure only survived the deadly attack because he was home working at that time, reports by Agence France Presse (AFP) indicated.

The suspect casually walked away and local police seemed paralysed in pursuing him despite leads provided by a witness, who detailed the physical appearance of Mr Breivik.

The tip was wasted altogether as "communication problems, failure to follow procedures and inadequate means," bogged down police reaction and operation regarding the emergency incident, the report said.

And while Oslo was at loss on how to handle the whole episode, Mr Breivik took a boat and proceeded to Utoeya Island, which was mere 600 metres away from the capital.

There, the self-declared nationalist militant attacked a youth camp sponsored by the government, where he mowed down teenage boys and girls with automatic weapons and hand guns.

The final death toll after the last shot was fired in the terrorised island: 69, excluding the hundreds that were wounded during the combined attacks, media reports said.

For what looked like an eternity, Mr Breivik gunned down young kids and the police were nowhere in sight because boats and helicopters were inoperable or unavailable, the commission report lamented.

First gripe by the commission was failure on the part of Norway's intelligence agency, which did not raise a red flag as Mr Breivik started stockpiling materials that would enable to concoct a bomb.

And following authorities' failure to pre-empt the attack on the capital, the gunman perpetrated his attacks on hapless kids afterwards without the government effectively getting in his way.

"The authorities' ability to protect the people on Utoeya Island failed. A more rapid police operation was a realistic possibility. The perpetrator could have been stopped earlier on 22 July," the report said.

What had transpired on that unfortunate day "revealed serious shortfalls in society's emergency preparedness and ability to avert threats," the 10-member commission stressed.

"The challenges turned out to be ascribable to leadership and communication to a far greater extent than to the lack of response personnel," Reuters reported the report's stinging assessment of incident as saying.

In a reaction, Mr Stoltenberg took the report as very important "because it gives us facts and knowledge and understanding of what happened."

"It took too long to apprehend the perpetrator and the police should have been on Utoeya earlier. This is something I regret," he admitted, adding that he takes full responsibility for what had happened.

The report came out more than a week prior to handing the down court verdict on Mr Breivik, who faces the prospect of spending a lifetime behind bars either in a mental or prison facility.