CHICAGO -- Commuter trains on the Metra Milwaukee District North and West lines were back on schedule by early afternoon after a "minor" derailment today at the north end of Union Station in downtown Chicago, Metra officials said.

At one point this morning, trains were running 30 to 40 minutes behind schedule as a result of the derailment, reports the Chicago Tribune.

A West line express train that originated in Roselle, stopping in Franklin Park and then running nonstop to Western Avenue, derailed at 8:20 a.m., said Metra spokesman Tom Miller. No injuries were reported, he said.

"The front wheels came off the tracks," Miller said. "The cause of the minor derailment is unknown."

The train came to a halt, and Metra personnel helped passengers off within 20 minutes of the incident, Miller said. Crews put the train back on the tracks and made necessary repairs by about noon, and full service was restored shortly thereafter.