Police said an air ambulance had been called in to transport victims to hospitals “due to the severity of the injuries”.
There was no information on the identities or nationalities of those involved in the crash.
Residents quoted by media said the road is usually busy because it leads to one of the entrances to Yellowstone.
Millions of tourists – domestic and international – travel every year to Yellowstone, the first national park to be established in the United States.
It covers portions of Wyoming, Idaho and Montana and is home to thousands of geothermal features – hot springs, mudpots, steam vents and about half the world’s active geysers, including Old Faithful.
– Agence France-Presse