SPRINGFIELD TOWNSHIP, Mich. -- Two freight trains crashed head-on on Thursday, killing two men, injuring two others and forcing the evacuation of nearby homes and schools, a wire service reports.

The evacuation order was lifted about five hours after the fiery wreck when authorities determined that cars containing chemicals had not leaked. About 3,000 gallons of diesel fuel were spilled.

Investigators were looking into whether there was a malfunction at a nearby switching yard or whether severe weather the night before may have played a role in the crash, said Oakland County Undersheriff Thomas Quisenberry.

"It's amazing how many cars did not get upset or derailed," he said.

The wreck occurred at 5:55 a.m. about 25 miles northwest of Detroit, on a track operated by Grand Trunk, a subsidiary of Canadian National railroad, officials said.

About 12 families were evacuated from their homes and several nearby schools were closed, authorities said.

Mary O'Daniel, whose house is near the tracks, said she heard one train pass, then another.

"As the (second) train was going through, there was a rumbling and then all of a sudden, boom, boom, boom, boom," she said.

Two men on the northbound train were killed, and two men on the southbound train were critically injured and trapped in the wreckage for about three hours. They were conscious when taken from the train and sent by helicopter to a hospital.

Gloria Combe, a railroad spokeswoman, said a conductor and engineer were killed, but their names were being withheld until their families were notified. The injured also were a conductor and an engineer, she said.

Railroad spokesman Jack Burke said he believed one train car contained chloride gas.

The National Transportation Safety Board planned to investigate, and Quisenberry said an FBI representative was also at the site.