(CNN) -- A U.S. team was at work Monday at a Himalayan military outpost in Pakistan, joining the search for as many as 139 people buried in a massive avalanche.
The eight-member U.S. group of experts arrived Sunday, the official news agency Associated Press of Pakistan (APP) reported.
Three experts from Switzerland and six from Germany were on their way to Pakistan on Monday as well, according to the Pakistani military.
About 300 Pakistani soldiers and civilians were working at the rescue site, using heavy machinery and helicopters, the military said.
APP said around 124 troops and 11 civilians could be trapped. The military said Sunday that as many as 139 people were believed trapped.
A blanket of rock and snow covering one square kilometer -- about the size of a large city block -- slid over the base on the Siachen glacier near the Indian border on Saturday morning, burying it under 70 feet of snow.
It was the first such disaster at the mountain headquarters in its two decades of existence, the military said.
The U.S. Embassy in Islamabad expressed condolences for those who have lost their lives, and offered "any assistance that Pakistan requires in the aftermath of this tragedy."