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A hiker was killed and four others injured when ice caves on a remote Washington state mountainside partly collapsed, authorities said Monday night.

Three of the injured were were airlifted to hospital with serious injuries after the accident at the Big Four Ice Caves in Mount Baker-Snoqualmie National Forest.

The body of the hiker could not immediately be recovered because of the "fragile nature of the ice," Snohomish County spokeswoman Shari Ireton said.

Survivor Chloe Jakubowski, 18, escaped from the cave and went to alert emergency services.

“There was a loud pop above us," she told NBC News. "Once I saw the ice chunks falling I ducked for cover and held my hands over my head."

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A woman next to her was unconscious, she said.

It was the second straight day that part of the ice caves — which are accessible only by a 26-mile narrow, winding road — collapsed on Big Four Mountain, about 20 miles east of the town of Granite Falls. No one was injured in Sunday's collapse, which a visitor captured on video.

The caves are formed when runoff from melting snow hollows out a tunnel in snow mounds that slide off the mountain and collect at the base of a cliff. The main cave, nearly 100 feet deep and 25 feet wide, is among the most popular hiking destinations in the Cascade Mountains.

But authorities have long warned that the caves are dangerous, because when temperatures rise, they can fall apart in giant ice mounds.

Susan Gregg, a spokeswoman for Harborview Medical Center in Seattle, said the hospital was treating two males for head lacerations and leg and pelvis fractures. A female patient arrived shortly afterward.

All the injured were conscious, but one man, 25, was in critical condition, Gregg said. A second man, 35, was in serious condition and the woman, 35, was in satisfactory condition.

One girl who was not seriously injured in the collapse was transported by ground and being treated at Providence Medical Center in Everett.

Snohomish County emergency officials said the area around the Big Four ice caves would remain closed until search and rescue teams could assess the safety of the caves and recover the deceased victim of the collapse.

Temperatures reached 80 degrees in the area of the caves Monday as Washington swelters through a heat wave. The heat led the U.S. Forest Service to issue a special warning in May alerting hikers that the main cave was in a "dangerous state ... large, inviting and collapsing," and urging them to stay out of it. Several signs along the trail warn people to steer clear.