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KATHMANDU (Reuters) - Rescuers began digging through several feet snow at two mountainside locations in Nepal on Tuesday where four South Korean trekkers and three Nepali guides are thought to be trapped, officials said.

The hikers have been missing since Friday, after being swept away by an avalanche during a trek in the region of Mount Annapurna, the world’s tenth highest mountain.

Nepal Tourism Board official Nandini Thapa said army rescuers, who were ferried in by helicopter, had already started digging.

“It is very deep ice and the work would take time,” Thapa said.

Army official Gokul Bhandari said the nine rescuers would spend the night there and continue the search early on Wednesday.

The operation could take several weeks as the avalanche had dumped up to 12 feet (3.6 meters) at the site of the disaster, about 150 km (90 miles) northwest of the capital Kathmandu, rescuer Bijay K.C. said.

The incident comes as the winter trekking season in Nepal, home to eight of the world’s 14 highest mountains, including Mount Everest, is drawing to a close this month.

In 2018, five South Koreans and four Nepali guides on a Himalayan climbing expedition were flung to their deaths after a huge block of ice crashed over a cliff into a narrow mountain gorge.