Three people were seriously injured by the Bergen slide and two, a 27-year-old woman and a three-year-old girl, were in critical condition after a 40-meter (131-foot) wide cliff face gave way over a row of homes, hitting at least eight houses. A 51-year-old woman was found dead.
One mother told newspaper Bergens Tidende that she had to throw her children out of a second story window to get them out of the house quickly as the cliff face flooded into the lower section of their home.
A geologist has investigated the accident site at Fana in southern Bergen and advised rescue workers to exercise extreme caution.
A state of disaster alert has been declared at Haukeland University Hospital and the area was being secured in order to search for further possible victims.
Police could not rule out the possibility that further victims were missing, trapped in the avalanche of earth, stone and trees on early Wednesday morning. Police were also uncertain about how best to secure the area, which is near highway E39.
"The most important thing now is to safeguard those in the slide area. We must be extremely careful and cannot, for example, use heavy machinery in the area," said police operation leader Harald Lekven.
As rescue efforts began police had avalanche dogs on site and aid workers were digging in the landslide with shovels and pickaxes. Reports of sounds from houses hit and destroyed by the avalanche created concerns that more people could be trapped in their earth-filled homes.
Residents in the area were quickly evacuated. About 75 were driven to nearby hotels and another 25 sought refuge with neighbors.