- Some 700 people evacuated from the affected area.
- Ground made of clay, area not stable.
- "This is a big catastrophe" - PM Erna Solberg.
OSLO: Ten people were injured, one of them critically, and 21 people remained unaccounted for after a landslide in southern Norway swept away more than a dozen buildings in the early hours of Wednesday, police said.
The landslide struck a residential area in the municipality of Gjerdrum, some 30 km (19 miles) north of the capital Oslo.
Photos of the site showed a large crater with destroyed buildings at the bottom of it. Other buildings hung on the edges of the crater.
Helicopters hovered over the area, at times lowering emergency responders towards the debris of collapsed houses, TV footage showed.
Around 700 people have been evacuated from the area so far, police said.
"There were two massive tremors that lasted for a long while and I assumed it was snow being cleared or something like that," Oeystein Gjerdrum, 68, told broadcaster NRK.
"Then the power suddenly went out, and a neighbour came to the door and said we needed to evacuate, so I woke up my three grandchildren and told them to get dressed quickly."
The missing people were from homes in the innermost area of the landslide but it was not immediately clear whether they had been trapped in their houses, were away at the time or had managed to escape, the police said.
"There are many who are still unaccounted for. This is a big catastrophe," Prime Minister Erna Solberg told reporters during a visit to the site.
The area remains unstable for now and can only be accessed by helicopter, said Roger Pettersen, head of the police operation at the site.
Masses of earth are continuing to move in what has been one of the largest clay slides in recent Norwegian history, Torild Hofshagen, the regional head of the Norwegian Water Resources and Energy Directorate, told a news conference.
Southern Norway has seen large amounts of precipitation in recent days, which may have caused the clay soil prevalent in the area to shift, broadcaster NRK said.