Some 50 roads were also shut and two railway lines were closed because of the flooding and landslides.
Southeastern Norway has experienced several days of heavy rains. On Wednesday, the region registered some 60 millimetres (2.4 inches) of rain, and meteorologists predicted an additional 30 millimetres for Thursday in regions already hard hit.
The geographic spread of the flooding made it difficult for authorities to provide an exact tally of how many people had been evacuated, but media reports suggested the figure was around 500.
In the southeastern town of Kvam, ravaged by the rising floodwaters, some 250 people were forced to leave their homes.
While the flooding caused significant material damage, no injuries or deaths were reported.