An explosion that levelled a building at a Pickering Water Treatment plant — only blocks away from the city's Nuclear power plant — east of Toronto is being investigated by the Ontario Fire Marshal.

The explosion happened after 10 a.m. at the Duffin Creek Water Pollution Control Plant on MacKay Road, about 40 kilometres east of Toronto.

Pickering water

The area around Duffin Creek Water Pollution Control Plant on MacKay Road, about 40 kilometres east of Toronto, affected by explosion. (Google/CBC)

Images from the scene showed smoke in the sky above the plant. Firefighters were able to quickly bring the fire under control. There were no injuries.

However, given the plant’s proximity to the Pickering Nuclear Generating Station, the blast had a lot of people very shaken up.

The loud explosion left Donnie MacCharles and Terry Weldanks, who work across the street from the Duffin Creek Water Pollution Control Plant, fearing for their lives.

“We both looked back and saw a huge mushroom cloud,” Weldanks said.

“We thought it was all over for us because it was so loud and so intense,” MacCharles added.

The actual cause of the blast was likely a result of methane build up, according to Clifford Curtis,  Commissioner of Works for Durham Region.

The explosion took place inside the odour control building, where emissions are treated before being released into the air. Luckily, the building was empty.