Stuart Brideaux with Alberta Health Services says three were stable and went to a hospital in nearby Banff.
He had no information on the fourth patient.
The crash happened on Highway 93 near Hector Lake, about 20 kilometres north of Lake Louise.
RCMP say the bus is operated by Brewster Transportation based out of Banff.
Mounties say the driver of the bus was not injured and there were no passengers on the bus at the time.