More than 10,000 visitors were ordered out of Yellowstone as unprecedented flooding tore through the northern half of the nation's oldest national park - washing out bridges and roads and sweeping an employee bunkhouse miles downstream, officials said.

The only visitors left in the massive park straddling three states were a dozen campers still making their way out of the backcountry. No injuries have been reported.

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 Mr 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 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 marvelling 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 chocolate brown torrent that washed away everything in its path.

"It is just the scariest river ever," Kate Gomez of Santa Fe, New Mexico, said on Tuesday.

"Anything that falls into that river is gone."

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.

Mr Sholly said the backpackers who remained in the park had been contacted.

Crews were prepared to evacuate them by helicopter, but that has not been needed yet, he said.

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

Ms Gomez and her husband were among hundreds of tourists stuck in Gardiner, Montana, a town of about 800 residents at the park's north entrance.

The town was cut off for more than a day until Tuesday afternoon, when crews reopened part of a washed away two-lane road.

While the flooding cannot directly be attributed to climate change, it came as the Midwest and East Coast sizzle from a heat wave and other parts of the west burn from an early wildfire season amid a persistent drought that has increased the frequency and intensity of fires that are having broader impacts.

Smoke from a fire in the mountains of Flagstaff, Arizona, could be seen in Colorado.

Rick Thoman, a climate specialist at the University of Alaska Fairbanks, said a warming environment makes extreme weather events more likely than they would have been "without the warming that human activity has caused".

"Will Yellowstone have a repeat of this in five or even 50 years? Maybe not, but somewhere will have something equivalent or even more extreme," he said.

Heavy rain on top of melting mountain snow pushed the Yellowstone, Stillwater and Clarks Fork rivers to record levels on Monday, according to the National Weather Service.

Officials in Yellowstone and in several southern Montana counties were assessing damage from the storms, which also triggered mudslides and rockslides.

Some of the worst damage happened in the northern part of the park and Yellowstone's gateway communities in southern Montana.

National Park Service photos showed mud and rock slides, washed out bridges and roads undercut by churning floodwaters of the Gardner and Lamar rivers.

In Red Lodge, Montana, a town of 2,100 that is a popular jumping-off point for a scenic, winding route into the Yellowstone high country, a creek running through town jumped its banks and swamped the main thoroughfare, leaving trout swimming in the street a day later under sunny skies.

At least 200 homes flooded in the city and in Fromberg, Carbon County authorities said.

Residents described a harrowing scene where the water went from a trickle to a torrent over just a few hours.

The water toppled telephone poles, knocked over fences and carved deep fissures in the ground through a neighbourhood of hundreds of houses.

Power was restored by Tuesday, though there was still no running water in the affected neighbourhood.

Heidi Hoffman left early on Monday to buy a sump pump in Billings, but by the time she returned her basement was full of water.

"We lost all our belongings in the basement," Ms Hoffman said as the pump removed a steady stream of water into her muddy backyard.

"Yearbooks, pictures, clothes, furniture. We're going to be cleaning up for a long time."

On Monday, Yellowstone officials evacuated the northern part of the park, where roads may remain impassable for a substantial length of time, Mr Sholly said.

But the flooding affected the rest of the park, too, with park officials warning of yet higher flooding and potential problems with water supplies and wastewater systems at developed areas.

The rains hit just as area hotels have filled up in recent weeks with summer tourists.

More than four million visitors were tallied by the park last year.

The wave of tourists does not abate until the autumn, and June is typically one of Yellowstone's busiest months.

It was unclear how many visitors to the region remained stranded, or how many people who live outside the park were rescued and evacuated.

Mark Taylor, owner and chief pilot of Rocky Mountain Rotors, said his company airlifted about 40 paying customers over the past two days from Gardiner, including two women who were "very pregnant".

Mr Taylor spoke as he ferried a family of four adults from Texas, who wanted to do some more sightseeing before heading home.

"I imagine they're going to rent a car and they're going to go check out some other parts of Montana - somewhere drier," he said.

At a cabin in Gardiner, Parker Manning of Terre Haute, Indiana, got an up-close view of the roiling Yellowstone River floodwaters just outside his door.

Entire trees and even a lone kayaker floated by.

In early evening, he shot video as the waters ate away at the opposite bank where a large brown house that had been home to park employees, who had evacuated, was precariously perched.

In a large cracking sound heard over the river's roar, the house tipped into the waters and was pulled into the current.

Mr Sholly said it floated five miles before sinking.

In south-central Montana, flooding on the Stillwater River stranded 68 people at a campground.

Stillwater County Emergency Services agencies and Stillwater Mine crews rescued people on Monday from the Woodbine Campground by raft.

Some roads in the area were closed and residents were evacuated.

The towns of Cooke City and Silvergate, just east of the park, were also isolated by floodwaters.

In Livingston, residents in low-lying neighbourhoods were told to leave and the city's hospital was evacuated as a precaution after its driveway flooded.

Officials in Park County, which includes Gardiner and Cooke City, said extensive flooding throughout the county had made drinking water unsafe in many areas.

The Montana National Guard said on Monday it sent two helicopters to southern Montana to help with evacuations.

In the hamlet of Nye, at least four cabins washed into the Stillwater River, said Shelley Blazina, including one she owned.

"It was my sanctuary," she said on Tuesday.

"Yesterday I was in shock. Today I'm just in intense sadness."

The Yellowstone River at Corwin Springs crested at 13.88ft on Monday, higher than the previous record of 11.5ft set in 1918, according to the National Weather Service.

Yellowstone got 2.5in of rain on Saturday, Sunday and into Monday.

The Beartooth Mountains north-east of Yellowstone got as much as four inches, according to the National Weather Service.