Several people have been injured in the partial collapse of an ice cave in Washington state that officials had warned was too dangerous for exploration due to unseasonably warm weather.

A spokeswoman from the Snohomish County Sheriff's Office said rescue workers were still trying to confirm how many people were in the Big Four Ice Caves near Granite Falls, 64km north of Seattle, when a cave gave way yesterday.

The Everett Herald reported nine people were injured, citing a figure from the US Forest Service.

Granite Falls ice cave collapse

The injured were all taken to local hospitals, the newspaper said.

The caves are home to a popular hiking trail and are part of the Mt. Baker-Snoqualmie National Forest.

In May, the US Forest Service warned hikers against entering the Big Four Ice Caves after several sections collapsed in unusually warm spring temperatures in the Pacific Northwest.