All Yellowstone National Park entrances have been closed in the wake of "unprecedented" rainfall causing "substantial flooding, rockslides and mudslides on roadways," the National Park Service announced Monday, with the northern entrance likely to remain closed through the rest of the season.
Some roads have been washed out and others are covered in mud or rocks, according to the park service. Power has also been knocked out in multiple parts of the park, officials said.
Park Superintendent Cam Sholly described it as "record flooding."
In an update Tuesday night, the National Park Service said the northern portion of the park is "likely to remain closed for a substantial length of time due to severely damaged, impacted infrastructure."
The flooding was sparked by up to 3 inches of rain amid near-record-high temperatures that melted 5 inches of high-elevation snow over the weekend, Montana’s Park County Sheriff's Office officials said Tuesday during a press conference. Rivers are at peak levels now and are forecast to recede in the next few days.
With 12 inches of snowpack left, Yellowstone "could have another flood event" in the upcoming four to five days, Sholly told reporters Tuesday evening.
MORE: Are rising water prices amid the Western megadrought inevitable? Yes, but it's complicated, experts sayAll front country visitors have left the park, though there are still some people in the backcountry that they are working to get out, park officials said Tuesday.
Between 15,000 to 20,000 visitors were in the park before flooding started. Several thousand visitors that were stranded in Gardiner have been evacuated, officials said.
Park officials likely won't be able to assess the full damage to get an idea of a reopening timeline until next week, when conditions are less dangerous, Sholly said.
The most significant damage appears to be in the northern range of the park, particularly between Gardiner, Montana, and Mammoth Hot Springs, Wyoming, Sholly said.
The park service warned that many roads could be closed "for an extended period of time." Hundreds of bridges will also need to be assessed, Sholly said.
The road between Gardiner and Cooke City, Montana, on the northern edge of the park will likely be closed for the remainder of the season -- which is about the end of October, Sholly said.
Park officials are exploring how soon they can reopen the southern part of the park to visitors.
The massive national park spans 2,219,789 acres, mostly in Wyoming but also in neighboring Montana and Idaho. Summer is the park's busiest tourist season.
The park closed for nearly two months in 2020 due to the COVID-19 pandemic. Park officials believe this is the first time Yellowstone has closed due to flooding.
ABC News' Max Golembo, Dan Peck and Aliyah Thomas contributed to this report.