The helicopter has been identified as a Russian Mi-17

The helicopter lost radio contact during bad weather after it took off in a mountainous district on Saturday.

Bad weather has hampered an air and ground search for the crafts by rescue helicopters and workers.

It is still not clear if the helicopter crashed or was able to make an emergency landing.

Officials said rain and low visibility were hampering efforts to find the helicopter, missing since noon local time (0615 GMT) on Saturday.

"It is continuously raining and very thick fog is covering the area with no sign of any let-up," a senior official, Hem Nath Dawadi, told the Reuters news agency.

Multiple nationalities

Seven WWF employees are among the missing, including four Nepalis, an Australian, a Canadian and an American, the organisation said.

Also listed among the missing are a Finnish diplomat, a US aid-worker and two Russian crew members as well as Nepalese officials and reporters.

A team of 90 soldiers and policemen has also been sent to the area on foot to help another ground team already there.

The helicopter party was returning from a landmark ceremony to hand over the Kangenjunga conservation area from the government to the local community.

The helicopter, identified as a Russian-made Mi-17, had been on a 20-minute flight to a local airport, where the passengers had been due to take a flight to the capital, Kathmandu.