The Associated Press

GRAETTINGER, Ia. — Environmental experts were checking for ethanol leaks Friday after a freight train derailed and burst into flames as it crossed a trestle bridge over a northwest Iowa creek that empties into the Des Moines River.

The derailment happened around 1 a.m. near the small community of Graettinger, about 160 miles northwest of Des Moines, the Palo Alto County Sheriff's Office said in a news release. It said two crew members escaped unharmed and no injuries have been reported. Officials asked area residents to evacuate, although they acknowledged that no one appeared to live within a half mile of the rural site.

Palo Alto County emergency management director Mark Hunefeld said at least 27 of 101 cars derailed. Several of the cars were still burning at noon and officials plan to let the fire burn itself out, although that decision will be reviewed later Friday afternoon, Hunefeld said.

Railroad personnel were able to unhitch 74 loaded tankers and move them away from the site.

VIDEO from Sioux City's KTIV: Freight train derailment and fire in Palo Alto County, Iowa

Iowa Natural Resources Department field office supervisor Ken Hessenius said he doesn't yet know whether any ethanol leaked into Jack Creek. Each tanker carries about 25,000 gallons.

Ethanol is water-soluble, will quickly disperse through surface water and can reduce oxygen content to the point of producing fish kills. The threat to drinking water depends on concentration, experts say.

Sasha Forsen, spokeswoman for Green Plains Inc. in Omaha, Nebraska, said the tanks had been filled with ethanol at the company's plant in Superior, Iowa. She declined to say where the shipment was heading.

Raquel Espinoza, a spokeswoman for Union Pacific, confirmed that the train was operated by that railroad company, but she declined to say more, referring questions to the National Transportation Safety Board.

NTSB spokesman Keith Holloway said agency investigators would be at the derailment site to determine the cause of the accident Friday afternoon.

Ethanol is an alcohol-based fuel additive that is highly flammable when exposed to air and an ignition source, such as a flame or spark.

A news release from the NTSB said initial reports indicated the rail cars that derailed Friday are older, less sturdy tanks. The government has ordered that such tanks be either retrofitted to higher standards or taken out of commission by 2029. The rail tanker standards were changed in 2015.

There have been at least seven significant accidents involving trains hauling ethanol since 2006 that released a combined 2 million gallons of the fuel. Among them was a July 2009 accident in Cherry Valley, Ill., that killed a woman and injured nine people, including two firefighters, when a Canadian National Railway Co. train derailed at a highway crossing and burst into flames.