Norway's parliament was briefly evacuated on Thursday after a minor explosion in an electrical room, but no one was hurt, the parliament said.
Police confirmed that a short circuit had occurred in an electrical system which caused a plume of smoke and a power outage at the building in central Oslo.
"The parliament building was evacuated because of an explosive short circuit in a technical room," parliament said on its Twitter account. "No injuries were reported."
Power was restored after a few minutes, and the building was reopened shortly afterwards, it said.
Security has been heightened in Norway since the twin attacks by right-wing extremist Anders Behring Breivik in July 2011 that left 77 people dead.
MP Per Sandberg told television news channel TV2 Nyhetskanalen that his colleagues spoke of hearing a "rumbling" and then "vibrations".
Several media outlets had earlier reported an explosion in a manhole just outside the parliament building, with one witness telling TV2 she saw a fireball that threw a manhole cover into the air.
Television footage showed police and firemen inspecting a sewage canal.
There was no sign of panic, although ambulances were sent to the area.
Authorities also cordoned off the scene to keep passersby at bay.