A large explosion has hit near the government headquarters in the Norwegian capital Oslo. The office of Prime Minister Jens Stoltenberg and a number of other buildings are reported to be damaged in the blasts. According to local media, the Prime Minister is safe. However, witnesses said at least eight people were injured in the city centre explosion. According to reports, all roads into the city centre have been closed. Television images showed rubble in the street and smoke around some buildings. The cause and exact location of the blast is not yet clear.