Updated at 12:30 p.m. with additional detail

EUGENE --Rail officials are investigating after 13 cars on a Union Pacific train derailed in Eugene.

Eugene police and Eugene Springfield Fire personnel were called when a black tanker car fell to its side Sunday in west Eugene on the Union Pacific tracks, The Register-Guard reported. Another 10 empty rail cars were behind the tanker, tilted at awkward angles. Two grain cars also derailed.

Union Pacific spokesman Justin Jacobs said the train was headed around a curve when the cars left the track.

"The main line wasn't affected, and there was no release (of any hazardous material)," he said.

Emergency responders kept traffic and residents away from the tracks because of concerns about the flammable liquid that was in the tanker car.

"We want to make sure we don't have a hazmat leak," said Battalion Chief Jeff Kronser of Eugene Springfield Fire.

Jacobs said Union Pacific will not know what caused the derailment until its investigation is completed.

Despite not being on the main track, the derailment delayed passenger train service.

Some residents near the tracks saw the derailment. Debbie Holte said she and her mother were on a walk when they heard a train pass and then suddenly stop.

"We didn't even hear anything," Holte said. "So we were surprised (to see the derailment.)"

-- The Associated Press