A bridge crossing the Yellowstone River in rural Montana has collapsed, plunging a freight train carrying hazardous materials into the water below sparking fears of a spill.
The freight train cars were carrying asphalt and sulfur, according to Stillwater County's chief of emergency services, David Stamey.
Drinking water intakes downstream have been shut down by officials while the danger is being assessed.
Three of the railcars that derailed were carrying hot asphalt, and four were carrying molten sulfur according to KC Williams, director of Emergency Management for Yellowstone County.
It's thought the incident happened at around 6.45am local time as the train was travelling westbound.
A reporter on the scene says they witnessed a yellow substance coming out of some of the tank cars. Though Mr Stamey has said there is no immediate danger for crews working at the site, and any hazardous material spilt into the water was being diluted by the swollen river.
In total, there were eight rail cars in the river or on the part of the bridge which collapsed. In a statement, Montana Rail Link spokesperson Andy Garland said the train crew were safe and there were no injuries reported.
Crews were at the scene near the town of Columbus, about 40 miles west of Billings. It's a sparsely populated area of the Yellowstone River Valley, surrounded by ranch and farmland. The river flows away from Yellowstone National Park, which lies about 110 miles southwest.
"We are committed to addressing any potential impacts to the area as a result of this incident and working to understand the reasons behind the accident," said Mr Garland.
Officials in neighbouring Yellowstone County said they had instigated emergency measures at water treatment plants due to the "potential hazmat spill" and asked residents to try and conserve water.
There's an investigation ongoing into the cause of the collapse. The river levels were high with heavy rains, but it's unclear whether that was a factor or not.
The Montana Disaster Emergency Services has been notified, Federal Railroad Administration officials were also at the scene. State officials are advising the public to avoid parts of the river due to "potential contaminents".
Kelly Hitchcock of the Columbus Water Users shut off the flow of river water into an irrigation ditch downstream from the collapsed bridge in order to prevent the contents from the tank cars reaching nearby farmland. She said the Stillwater County Sheriff's Office called them on Saturday morning to warn about the collapse.
The Yellowstone saw record flooding last year that caused extensive damage to Yellowstone National Park and adjacent towns in Montana. The US Environmental Protection Agency noted that sulfur is a common element used as a fertiliser as well as an insecticide, fungicide and rodenticide.
