The death toll from an avalanche on Mount Everest has risen to 12. All those killed are thought to be Nepalese guides who had been fixing ropes for other climbers.

It is the worst single incident ever on the mountain. The avalanche hit the area just below Camp 2 at 21,000 feet.

Nepalese tourism ministry spokesman Mohan Krishna Sapkota has said five people are still missing.

Helicopters and rescuers on foot have been sent to the scene on the most popular route to the summit.

Ang Tshering, of the Nepal Mountaineering Association, said the area where the avalanche occurred is known as the "popcorn field".

Hundreds of climbers and guides have gathered at the base camp ahead of their attempt to scale the 29,035-foot mountain.

They have been setting up camps ahead of the peak climbing season at the start of May when the weather is more favourable.

Nepal has announced several steps this year to manage the flow of climbers, minimise congestion and speed up rescue operations.

Preparations include sending officials and security personnel to the base camp at 5,300m (17,380ft), where they will stay until the end of the climbing season in May.

More than 4,000 climbers have scaled the summit since 1953, when it was first conquered by Edmund Hillary and Sherpa Tenzing Norgay.

More than 300 people are believed to have died tackling the peak during that time.