Tank cars loaded with thousands of gallons of highly flammable ethanol exploded in flames as a freight train derailed, killing one person and forcing evacuations of hundreds of nearby homes.
Five tank cars continued burning Saturday morning and officials said they would wait for the "very dangerous" inferno to burn out by itself.
Rockford Fire Chief Derek Bergsten said 74 of the train's 114 cars were filled with ethanol, or ethyl alcohol.
At the height of the fire Friday night, 14 rail cars were ablaze, said Canadian National Railway Company spokesman Patrick Waldron.
Eighteen cars, all containing ethanol, left the tracks in the derailment about 9 p.m. Friday, Waldron said.
The cause of the derailment had not been determined. Reports that it was caused by a washout of the tracks following heavy rain were "not a certainty and this remains under investigation," Waldron said.
Officials evacuated the area on the edge of Rockford, about 80 miles northwest of Chicago, Friday night amid concerns about air pollution.
Winnebago County Coroner Sue Fiduccia said early Saturday the death was that of a female who was in a car waiting for the train to pass a crossing near the derailment site.
Bergsten said three other people ran from the car when it was bombarded with flying railroad ties and they were severely burned by flaming ethanol. They were taken to OSF Saint Anthony Medical Center in serious to critical condition, and one was transferred to Stroger Hospital in Chicago, he said.
Two crewmen on the eastbound Canadian National train escaped injury, Waldron said. The engine crew was able to pull 64 cars away from the scene.
Witnesses told the Rockford Register-Star that cars on the Chicago-bound train began hydroplaning in standing water as it approached the crossing. Some of them left the tracks moments before two of them exploded.
Parts of northern Illinois may have gotten as much as 4 inches of rain Friday, said meteorologist Gino Izzi of the National Weather Service. Chicago's O'Hare International Airport, 40 to 50 miles east of Rockford, measured 3.6 inches, a record for the date, he said.
Kirk Wilson, a fire chief in nearby Rockton, said he expected the ethanol to continue burning until later Saturday.
"We're letting the product burn itself out," he said. "We can't get too close to it. We're observing everything through binoculars from about 200 or 300 feet away."
"The situation is not under control, but we are making progress in getting it under control," said Wilson, whose department was one of at least 26 that went to the derailment scene. "It's very dangerous. It's very explosive. We're not risking any firefighters' lives."
Officials evacuated residents of about 600 homes within a half-mile of the derailment, Bergsten said. He said potentially toxic fumes should keep them out of their homes until environmental officials give them the green light to return.
"At first I thought it was a tornado because they always say a tornado sounds like a train coming," said Jeff Tilley, a Register-Star employee who lives near the scene of the derailment.
Alicia Zatkowski, a spokeswoman for ComEd, said the derailment knocked out power to about 1,000 of the Chicago-based utility's Rockford-area customers.
The derailment was being investigated by Canadian National and the Federal Railroad Administration. Members of the National Transportation Safety Board were en route early Saturday.