(CNN) -- Two people were killed and 21 others were injured Wednesday when a tour bus went out of control and overturned on a freeway outside Austin, Minnesota, state authorities said.
The bus, which was carrying senior citizens, overturned on Interstate 90 about three miles west of Austin, landing in a ditch off the right side of the roadway. At least 10 ambulances and several medical helicopters were called to the scene.
"All 23 people on board were either injured or killed," said Andy Skoogman, spokesman for the Minnesota Department of Public Safety.
Weather conditions were good when the bus, headed east, crossed the highway median, crossed over westbound lanes and overturned, Skoogman said.
The cause of the accident was not immediately known, he said. Investigators talked with some passengers, he said, but had not yet talked with the driver.
CNN affiliate KAAL reported the bus was returning to Rochester, Minnesota, from a trip to a casino in Northwood, Iowa.