The cleanup has begun at the site of a train derailment in Montana that caused a bridge across the Yellowstone River to collapse, Montana Rail Link said in a statement Sunday.

The company's railcars left the tracks Saturday morning in Stillwater County, sending multiple cars into the Yellowstone River. No injuries were reported.

Images of the incident showed a buckled bridge sitting in the water with the derailed cars.

Cleanup work and water sampling at the site began Saturday and is "ongoing," the statement said.

"Track repairs have been made enabling access to begin cleanup of the affected cars," Montana Rail Link said.

Some of the derailed cars carried molten sulfur and asphalt, and two cars contained sodium hydrogen sulfate, Montana Rail Link said in a statement Saturday.

Those two cars did not land in the river, according to the company, and initial air quality assessments found there was "no release event associated with those two cars."

The company said Sunday it continued "to closely monitor (and mitigate) all releases involving molten sulfur and asphalt" and its impacts to the site and nearby area.

"Both of these substances harden and solidify quickly when interacting with water, and modeling suggests that significant downstream movement of material is unlikely," according to the statement Sunday.

The company also said it is working with local and federal partners throughout the cleanup process, including the Montana Department of Environmental Quality and the Environmental Protection Agency.

"Montana Rail Link remains committed to addressing any potential impacts to the area as a result of this incident," the company said.