Why the Canadian Pacific Railway Ltd. trains collided is under investigation, said Mike LoVecchio, a spokesman for the rail company in Calgary, Alberta.
The trains crashed about 5:30 a.m. near Dresbach in southeastern Minnesota. One rail car struck a 1,000-gallon propane tank attached to a switching station, causing a small leak that was stopped by early afternoon, authorities said.
The crash involved a freight train with three locomotives, three loaded cars and 90 empty cars, and a shorter train called a "yard switcher" with two locomotives and 15 cars loaded with fertilizer, LoVecchio said.
Thirteen cars from each train derailed.
Three cars were leaking liquid nitrogen, a farm fertilizer, but the material was contained around the cars and none was reaching the river, he said.
LoVecchio said crews were working through the night on the cleanup, but it wasn't known when the line would reopen to traffic. Trains were able to detour over sister railways, he said.
About 25 disabled veterans at the nearby Mosher Veterans Rest Home near Dresbach were evacuated for several hours as a precaution because of the leak but returned home by late afternoon, said Joyce Tlougan, deputy director of Winona County Emergency Management.