Water continues to rampage over Highway 87 at Roundup inundating large portions of the town.
Water stood about 8 feet deep around the Busy Bee Cafe, a local landmark, as the ordinarily narrow river channel spread across the valley floor.
Highways into town from both Lavina and Billings remain closed.
UPDATE: Floodwaters of the Musselshell River have forced the evacuation of 30 homes in Roundup and the closure of Highway 87 between Roundup and Billings.
"The only way we've got to get out is to go to Forsyth and around," said Jeff Gates, Musselshell County Disaster and Emergency Services coordinator.
He said the county was attempting to set up a shelter for refugees, but "I can't get the Red Cross in here through the high water."
Temporary arrangements are being made with the local LDS church with overflow in the Community Center, he said.
The Musselshell has inundated the town from the highway bridge over the river to Laundry Hill, where the streets rise toward Main Street.
Gates said three feet of water was running over the highway in places.
"We're making a big lake up here," he said.
In addition to flooded homes, several business were in high water. Main Street has not been affected.
Many roads throughout the county have washed out and are impassible.
Associated Press Report:
The Musselshell River has put a central Montana town under an estimated 6 feet of water and people are cut off in isolated areas across the state as flooding continues to spread.
Roundup resident Cameron McCleary says water started coursing through the town early Thursday and is continuing to rise.
Authorities say the Musselshell River is expected to crest between Friday and Sunday.
More rain is forecast through the weekend as flood emergencies were announced in Jefferson, Sanders and Musselshell counties.
To the south, residents and officials in Carbon, Yellowstone and Big Horn counties continue to pump water from hundreds of flooded basements.