At least four people have been injured, one seriously, in an avalanche in a popular ski resort in the Swiss Alps.
The avalanche was reported at a marked slope in Crans-Montana at about 14:20 local time (13:20 GMT).
Officials have said that 240 rescuers are continuing to search the scene overnight.
Police have said they cannot discount the possibility that others still may be affected, after local reports said up to 12 people may have been involved.
“Witnesses have said that other people may be buried, and the search continues with considerable resources,” local police commander Christian Varone said at a news conference on Tuesday evening.
The avalanche engulfed 400m (1300ft) of piste marked out for skiers, Mr Varone said.
Search dogs and rescue helicopters have been mobilised to search for victims at the site.
An initial search with dogs was unsuccessful, local newspaper Le Nouvelliste reports.
Thousands were on the resort’s slopes at the time
The snow is compacted and is 2m deep in places, a rescuer was quoted as telling the newspaper.
Shock waves across the Alps
Analysis by Imogen Foulkes, BBC Geneva Correspondent
This was the avalanche that was never supposed to happen. Alpine villages, roads, railways and ski runs are all extensively risk mapped. Skiers caught up in avalanches tend to be off-piste, but this snow slide hit the lower stretch of a very popular slope.
It is too early to determine the cause, but serious questions will have to be answered about alpine safety.
It is half-term across much of Europe and the ski slopes are crowded with families. Eight thousand people were on Crans-Montana’s slopes when the avalanche struck.
An official investigation, involving rescue services, but also, significantly, weather experts, is already under way.
Just a few weeks ago there was heavy snow across the Alps, but the last few days have seen strong sunshine. Some are already asking whether this avalanche, unthinkable for many, might be connected to climate change.
Valais Public Prosecutor Catherine Seppey has opened an investigation into the reasons behind the avalanche.
Ms Seppey said it was not clear if the incident was triggered by skiers or by weather conditions.
Temperatures in the area have reportedly warmed in recent days, causing some snow to melt.
However, the avalanche risk in the region was set at only two out of five on Tuesday.
Crans-Montana is set to host two women’s World Cup races this weekend.
An emergency telephone number has been set up for families who think their loved ones might be involved.