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, about 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, with one house seen collapsing, TV footage showed.
Helicopters hovered over the area, at times lowering emergency responders towards the debris of collapsed houses.
About 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 clear whether they had been trapped in their houses, were away at the time or had managed to escape, the police said.
"It is a catastrophe," Prime Minister Erna Solberg told reporters after visiting the site.
"There could be people trapped... but at the same time we can't be sure because it is the New Year's holiday which means people could be elsewhere," she said, warning that rescue operations could take a long time.
"This could take days," she said. "The situation is still so unstable that it is impossible to do any [rescue] effort other than from helicopters."