I-84 is a major east-west highway through Oregon that follows the Columbia River Gorge.
Umatilla County Emergency Manager Jack Remillard said the bus was owned by Mi Joo travel in Vancouver, B.C., and state police said the bus was en route from Las Vegas to Vancouver.
A woman who answered the phone at a listing for the company confirmed with The Associated Press that it owned the bus and said it was on a tour of the Western U.S. She declined to give her name.
A bus safety website run by the U.S. Department of Transportation said Mi Joo Tour & Travel has six buses, none of which have been involved in any accidents in at least the past two years.
The bus crash was the second fatal accident on the same highway in Oregon on Sunday. A 69-year-old man died in a rollover accident about 30 miles west of the area where the bus crashed.
A spokesman for the American Bus Association said buses carry more than 700 million passengers a year in the United States.
"The industry as a whole is a very safe industry," said Dan Ronan of the Washington, D.C.,-based group. "There are only a handful of accidents every year. Comparatively speaking, we're the safest form of surface transportation."
The bus crash comes more than two months after another chartered tour bus in October veered off a highway in northern Arizona, killing the driver and injuring dozens of passengers who were mostly tourists from Asia and Europe. Authorities say the driver likely had a medical episode.