Aerial view of the explosion Twitter

The Norwegian Prime Minister's office in Oslo has been hit by an explosion, shattering windows and causing "deaths and injuries", according to Norwegian police.

Prime Minister Jens Stoltenberg is safe and nearby offices are apparently being evacuated after windows were blown out of the 17 storey building. ABC news have reported that US government sources have attributed the cause of the blast to a "massive vehicle bomb". According to NRK news network there have been two fatalities and dozens hospitalised.

According to Associated Press, a Norwegian official from the site has said that there are people "still trapped in buildings."

The epicentre of the blast was reportedly between a key government building and a national newspaper office. Athar Kaleem in Oslo told BBC (sic): "It was a massive explosion, I was at least 1km away from the scene but I felt the explosive in my feet. Everyone had the same feeling. It seems the explosion got very high shock waves as it broken the mirrors at quite larger distances. Now I am near the main place and city is in panic, grief and in tears."

Reports that the explosion could be the result of a burst gas pipe have been discredited due to Norway not having an extensive gas network.

The blast comes amid a series of terror plots in Norway that have been linked to al-Qaida.

Christian Aglen, a department manager at a Norwegian financial news website, reported on twitter: "Bomb in Oslo, Norway - this is undoubtedly one of the worst days in Norwegian history."

The following statement was added to the website of the Foreign and Comonwealth Office shortly after the incident: "An explosion has been reported outside the Prime Minister's office in Oslo. Further information will be added as soon as it is available."