At least four people have perished near the peak of Mount Everest this weekend, and the body count may yet rise according to unconfirmed reports from the site.

The four climbers — a German doctor, a Nepal-born Canadian citizen, a South Korean mountaineer, and a Chinese climber — died as a result of exhaustion and high-altitude sickness on their way down from the summit.

A major issue this year wreaking havoc on the health of Everest scalers is a phenomenon known as the "traffic jam."

A confluence of complications — late start to an already tight climbing season, a rise in the number of climbers looking to summit the mountain, and an overcrowding at the perilous "Hillary Step" leading to the top — has resulted in a life-threatening bottleneck that leaves climbers stranded at the summit for longer than is advisable.

"That's a hell of a lot of standing around," says experienced expeditionist Tom Briggs. "That certainly increases the dangers of frostbite and other problems like high-altitude sickness."

Some Sherpa guides are recalling the tragic climbing season of 1996 — the deadliest on record — in describing the dangers they've encountered this year.

Others say this is an all-together new threat. "This is the first time I've seen it like this," Onzchhu Sherpa told Outside Magazine.

Sadly, he may see it again soon: A new traffic jam is expected as some 200 climbers attempt to reach the summit this weekend.

[H/T: NPR, screengrab via Outside]