WAUSAU, Wis. (WSAU) – An investigation is underway into what caused a train derailment in Wausau last night.

The last three cars of a Canadian National freight train jumped the tracks on Townline Road about 6:30 p.m., said rail spokesman Patrick Waldron. One of them hit an office building at the railroad’s train yard.

All three cars were empty.

A cleaning worker in the building escaped injury – and authorities said there was damage to the walls and heating system. A railroad crossing signal was also knocked down.

Crews re-railed the train cars this afternoon.