KANSAS CITY, Mo. (AP) – Fire officials say a build-up of methane gas caused an explosion at a Kansas City wastewater treatment plant.

No injuries were reported.

Brooke Givens, spokeswoman for the city’s water department, said the Blue River Wastewater Treatment Plant was damaged by the Wednesday explosion but it remained in operation.

The explosion occurred near the plant’s rear door and damage was reported in the hallway and stairwell. A monetary damage estimate was not immediately available.

Methane gas is a byproduct of the wastewater treatment process. Givens says the cause of the explosion is being investigated.