4 Die in 4 Days Climbing Mount Everest

Climbers from Australia, India and the Netherlands were among those killed.

Meanwhile, two Indian climbers, Paresh Nath and Goutam Ghosh, have been missing on the mountain since Saturday. They were last seen near the legendary Everest summit, Wangchu Sherpa of the Trekking Camp Nepal agency in Kathmandu told The Associated Press.

The four deaths were the first reported this year on Everest as the busy trekking season nears its end. Two climbers died from altitude sickness, one fell to his death, and one is suspected of dying from a heart attack, CNN reported. The causes of deaths could not be independently confirmed by ABC News.

Rescue teams said there have been recurring calls of climbers suffering from altitude sickness, frostbite, falls and injuries.

The tourism industry, which brings in more than $3 million from Everest climbing fees alone, is Nepal’s chief source of foreign income and contributed almost 9 percent of its GDP in 2014, according to a report by the World Travel and Tourism Council. But the impoverished Himalayan country saw its tourist arrivals drop after deadly twin earthquakes and quake-triggered avalanches last year.

ABC News' Ishwar Rauniyar in Kathmandu contributed reporting.