Residents in the St. Mary’s Hospital area of Kitchener were startled Wednesday afternoon by an explosion at a water treatment plant.

The explosion occurred shortly before 5 p.m. Wednesday at 20 Greenbrook Drive.

Fire crews, including 15 firefighters and a hazmat team, responded to the scene moments later.

“There’s been some type of an explosion,” Kitchener Fire Chief Tim Beckett tells CTV News.

“Once they arrived, they found a strong chemical odour and some damage to the building.”

Officials believe the likely cause of the explosion was a delivery of ammonia accidentally being pumped into a chlorine tank.

“What we have been able to determine from the chemicals involved is (that) it doesn’t pose a health risk to the surrounding areas,” says Beckett.

Neighbours report hearing two explosions loud enough to shake their houses, and the smell of chlorine permeated the air in the minutes following the explosion.

“We were sitting in the living room … and just heard a huge bang. We couldn’t figure out what it was," neighbour Charles Love tells CTV News.

After hearing the noise, Love looked outside and noticed a "steam or mist" coming from the water treatment plant.

The blast was powerful enough to take out part of the structure's roof while also causing interior damage.

Greenbrook was closed between Stirling Avenue and Westmount Road as firefighters investigated the explosion.