Yellowstone floods force 10,000 to leave

More than 10,000 visitors have been ordered out of Yellowstone as unprecedented flooding tore through the northern half of the United States' oldest national park.

The flooding washed out bridges and roads and swept an employee bunkhouse kilometres downstream. Remarkably, no one was reported injured or killed.

The only visitors left in the massive park straddling three states on Tuesday were a dozen campers still making their way out of the back country.

Yellowstone National Park, which celebrates its 150th anniversary this year, could remain closed as long as a week, and northern entrances may not reopen this summer, Superintendent Cam Sholly said.

"The water is still raging," said Sholly, who noted that some weather forecasts include the possibility of additional flooding this weekend.

The Yellowstone River hit historic levels after days of rain and rapid snowmelt and wrought havoc across parts of southern Montana and northern Wyoming, where it washed away cabins, swamped small towns and knocked out power.

It hit the park just as a summer tourist season that draws millions of visitors was ramping up.

Instead of marveling at massive elk and bison, burbling thermal pools and the reliable blast of Old Faithful's geyser, tourists found themselves witnessing nature at its most unpredictable as the Yellowstone River river crested in a brown torrent that washed away everything in its path.

Waters were only starting to recede on Tuesday, and the full extent of the destruction may not be known for a while. It was not expected to have affected wildlife.

Closure of the northern part of the park will keep visitors from features that include Tower Fall, Mammoth Hot Springs and the Lamar Valley, which is known for viewing wildlife such as bears and wolves.

Old Faithful, Yellowstone Lake and viewing the Grand Canyon of the Yellowstone are on the park's southern loop road and likely to be reopened.

Sholly said he did not believe the park had ever shut down from flooding.