A US tour bus careered through a guard-rail along an icy road and several hundred feet down a steep embankment, killing nine people and injuring more than 20 others, authorities said.

The charter bus carrying about 40 people lost control on snow- and ice-covered lanes of Interstate 84 in a rural area of eastern Oregon, according to the Oregon State Police.

The bus crashed near the start of a seven-mile section of road that winds down a hill.

The bus came to rest at the bottom of a snowy slope and landed upright, with little or no debris visible around the crash site.

More than a dozen rescue workers descended the hill and used ropes to help retrieve people from the wreckage in freezing weather.

The bus driver was among the survivors, but had not yet spoken to police because of the severity of the injuries the driver had suffered.

Lieutenant Greg Hastings said the bus crashed along the west end of the Blue Mountains, and west of an area called Deadman Pass.

The area is so dangerous the state transportation department published specific warnings for truck drivers, advising it had "some of the most changeable and severe weather conditions in the Northwest" and can lead to slick conditions and poor visibility.

St Anthony Hospital in Pendleton treated 26 people from the accident, said hospital spokesman Larry Blanc. Five of those treated at St Anthony were transported to other facilities.

I-84 is a major east-west road through Oregon that follows the Columbia River Gorge.