Hazmat crews were still on the scene late Monday of a massive freight train derailment in Wisconsin northwest of Milwaukee.

Three engines and 19 cars from the Wisconsin Southern Railroad train overturned near Constitution and Independence avenues in Hartford, Wisconsin just after 9:30 a.m. Monday, CBS 58 in Milwaukee reported.

Three conductors went to an area hospital with minor injuries, Hartford Fire and Rescue Chief Tony Burgard told CBS 58.

Meanwhile, several thousand gallons of diesel fuel spilled into the ground — prompting several fire departments and emergency and environment management crews to respond to the scene.

A nitrous oxide tank also cracked, but has not leaked.

"We tried to make the leak as small as possible," Burgard told CBS 58. "There is a waterway, a tributary, that does lead into the Rubicon River. It looks like we are successful keeping all of the diesel fuel out of that tributary."

The cause of the derailment was under investigation late Monday, CBS 58 reported.

Police said it could take das to move the trains off the tracks.