Twenty-one people remain unaccounted for after a large landslide hit the village of Ask in southern Norway, police said on Wednesday.
The 21 unaccounted for are all thought to be local residents, Roger Pettersen, head of the police operation, told reporters.
"These could be people who are away visiting others, in the mountains. There may be people who have evacuated. But there may also be people who are inside the landslide area," he said.
The landslide hit Ask, a village of about 5,000 people around 40 kilometres north-west of Oslo, early in the morning. By mid-afternoon there had been no reports of fatalities.
Ten people were reported injured, including six who have been hospitalized with moderate injuries. Some were suffering from hypothermia, hospital officials said.
One area hit by the landslide remains so unstable that it can only be accessed by helicopter. Visibility is also reduced due to snowfall.
Visiting the scene along with Justice Minister Monica Maeland, Prime Minister Erna Solberg warned that the rescue operation could take several days.
"It is a dramatic experience to be here and see images from the scene of the accident and the whole landslide, and of course the knowledge that there are several that have not been accounted for," Solberg said.
Solberg's remarks were made after she was briefed by Pettersen and other officials at temporary headquarters set up in Ask to handle the incident.
More than 700 people have so far been evacuated, including residents of a nearby nursing home. Police warned residents not to return to the evacuated zone to collect personal items.
As a precaution, the evacuation zone was expanded due to issues with water and sewage lines.
The landslide, which is estimated to be 700 metres long and 300 metres wide, has been linked to quick clay, which is very unstable. A definitive cause has not yet been determined, according to geologists who have surveyed the scene from the air.
"This is one of the largest mudslides in recent years," said Torild Hofshagen of the Norwegian Water Resources and Energy Directorate.
Hofshagen told reporters the landslide could have been triggered by natural causes or excavation work.
Olav Gjerdingen, who lives about 150 metres from where the landslide hit, told public broadcaster NRK that police woke him and his wife at around 5 am (local time) and ordered to leave their home immediately.
Another evacuee, Oystein Gjerdrum, who was taking care of his grandchildren, managed to escape to safety with them.
"I woke up to the house shaking. I thought it was a plough truck or something... Then the power went off, and it got dark, and then the neighbour stormed in and said there has been a landslide and we have to evacuate," he told Oslo daily VG.
Police were alerted at around 4 am, triggering a large emergency operation with units from police, emergency services, the Red Cross and others.
Pettersen said that all available resources had been deployed, including helicopters and personnel from the home guard and military, who helped with evacuations.
The evacuees have been sent to a nearby hotel, where they were registered and offered assistance.
Local residents have also offered to open their homes and a nearby church offered crisis counselling.