Four people have died following an explosion at a waste water treatment plant near the southwest England city of Bristol, police said on Thursday. Three Wessex Water employees and one contractor died in the incident, which is not being treated as terror-related, Avon and Somerset Police Chief Inspector Mark Runacres said at a media briefing. A fifth person was injured during the explosion at the plant in the industrial area of Avonmouth, but the injuries are not considered life-threatening, Runacres said. “The fire service led the rescue operation but sadly, despite the best efforts of all those involved, we can confirm there have been four fatalities,” he said. Deeply saddened to learn that four people have lost their lives in the water works explosion in Avonmouth. Our hearts go out to the victims and their families. Thank you to the emergency services who attended the scene. — Boris Johnson (@BorisJohnson) December 3, 2020 Runacres would not speculate on the cause of the explosion. He said it took place in a silo holding organic matter from sewage before it “is recycled to land as an organic soil conditioner”. He said the explosion did not create any ongoing concerns for public safety. British Prime Minister Boris Johnson said “our hearts go out” to the victims and their families. Gas blast during prayers at Bangladesh mosque kills a least 16 “Deeply saddened to learn that four people have lost their lives in the water works explosion in Avonmouth,” Johnson said on Twitter. Wessex Water Chief Executive Colin Skellett said he was “devastated” by the incident, and the company is working to understand what happened and why. Sean Nolan, who witnessed the aftermath of the explosion, said he had heard a “boom and echo” and at first thought it was from a vehicle collision. The Avon Fire and Rescue Service was alerted at 11.22am to the “very challenging” incident in Avonmouth, located near Bristol, about 120 miles (195km) west of London. Six fire engines and rescue dogs were soon on the scene. “Luckily, our local fire station is not too far from here so we had crews in attendance very, very quickly and they were able to gain an element of situational awareness,” rescue service manager Luke Gazzard said.