Part of a freight train carrying ethanol derailed and caught fire in Columbus, Ohio, early Wednesday, shooting flames skyward into the darkness and prompting the evacuation of an area almost two kilometres wide as firefighters and hazardous materials crews monitored the blaze.

Norfolk Southern Corp. said it appeared about 11 cars of a southbound train derailed around 2 a.m. near Interstate 71, southeast of the Ohio State University campus. The train, traveling from Chicago to Linwood, N.C., went off the tracks north of downtown, in an industrial area blocks from residential neighborhoods.

Joel Priester said he watched the blast from his home two blocks away.

"I saw flames, then I heard a loud sound, like a boom, and saw the flames shooting higher," he said. "It looked like the sun exploded."

Three of the burning cars were tankers carrying ethanol, said Assistant Chief David Whiting of the Columbus fire division. After viewing the scene in daylight, authorities decided to let the fire burn out instead of trying to extinguish it.

It wasn't immediately clear what caused the derailment, which blocked access to about half of the Central Ohio Transit Authority's fleet of vehicles, limiting the city's public bus service. The National Transportation Safety Board said it was sending an investigator to the scene.

Two people who ran toward the scene before the explosion were injured but were able to take themselves to a hospital, fire Battalion Chief Michael Fowler said.

None of the three personnel onboard the train was hurt, Norfolk Southern spokesman Dave Pidgeon said. He said he couldn't comment on the crew's safety record but said the company has been recognized in the industry for its overall safety record.