The derailment and collapse into the Yellowstone River, near Billings, involved as many as eight cars, with those carrying molten sulfur and asphalt described as "compromised."

A train carrying hazardous materials derailed and a bridge collapsed into a southern Montana river Saturday, sending rail cars into the water and prompting concerns about contamination.

Some of those fears may have been allayed by evening as rail officials said two cars known to be carrying sodium hydro sulfate, which can burn, irritate and cause shortness of breath, had not entered the Yellowstone River below the failed bridge that used to span the waterway.

There was no release of hazardous materials from those particular railcars, said Andy Garland, spokesperson for Montana Rail Link.

But an unspecified number of other cars containing molten sulfur and asphalt had been “compromised,” he said in a statement.

Officials would continue to monitor the derailment site, he said.

No injuries were reported, officials said.

As many as eight cars had derailed, Columbus, Montana, Fire Chief Rich Cowger told NBC affiliate KULR of Billings.

Billings said it would shut down city water system intakes fed by the Yellowstone River for the time any pollutant would need to pass and end up downstream, according to a statement.

Billings, a city of nearly 110,000 people, has a clean supply of drinking water in its system, including storage tanks that are full, it said.

Laurel, Montana, suspended its intake from the river and temporarily shut down its water treatment plant Saturday morning, but a few hours later it reconnected its supply and restarted treatment, officials said in a statement.

Laurel officials visited the derailment site and investigated the water system, according to the statement.

Water treatment plants in Yellowstone County were working as normal as officials monitored the river for any signs of contaminants, county officials said in a statement.

“At this time there have been no reported negative impacts to Yellowstone County,” its government said in an afternoon statement.

The derailment and bridge collapse happened about 6 a.m. near the community of Reed Point, according to officials in Stillwater County, which abuts Yellowstone County. The bridge over the Yellowstone River was described as a rail bridge in the statement Saturday.

The National Transportation Safety Board said in a statement Saturday evening that it is sending an investigative team to the derailment site. The Federal Railroad Administration is leading the inquiry, the NTSB said.

It was not immediately clear if the collapse or derailment happened first or what caused either.

Asphalt contains carcinogens and has been linked to some forms of cancer. Molten sulfur can cause serous thermal burns upon contact and will form toxic and flammable gases when reacting to hydrocarbon, a compound at the heart of fossil fuels.