A search and rescue operation for the four South Korean trekkers and three Nepali guides missing after being struck by an avalanche in northwest Nepal could take weeks due to bad weather, rescuers said.

The area of last Friday's disaster lies along the popular Annapurna trekking route, about 150km northwest of the capital Kathmandu.

Tourism Department official Mira Acharya said seven rescuers from the Trekking Agents' Association of Nepal had reached the site with rescue equipment but could not begin the search due to new avalanches and rains.

"They are waiting for the weather to clear to start looking for the missing tourists," Acharya told Reuters, estimating the search operation could take 20 days.

One of the rescuers, Bijay K C, said that even if the weather cleared it would take several weeks for the snow to melt, hampering the overall operation.

Mount Annapurna is the world's 10th highest mountain at 8,091 metres (26,545 feet). Its base camp is known for its spectacular beauty and thousands of trekkers go there every year.

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

Last Saturday, four rescue helicopters evacuated 200 people, including 140 foreigner hikers, police officials said.

French trekker Herve Samonati, 60, arrived in Nepal for the Annapurna trek but said he was now heading to the neighbouring Mustang area, another popular trekking area.

"I wanted first to do the trek to the Annapurna base camp but decided not to go after the accident that happened recently because I find it too dangerous," he told Reuters via email.

- Reuters