Authorities have confirmed there are a "number of casualties" in the blast, which is believed to taken place in a chemical tank at a water recycling centre.
ADVERTISEMENTFour people have died and another injured after an explosion at a water recycling centre near Bristol, UK, police have confirmed.
The blast is believed to have taken place in one of the chemical tanks at Wessex Water’s Bristol water plant in Avonmouth.
UK police have declared a "major incident".
Emergency services were called to the site at Kings Weston Lane, Avonmouth, around 11.20 local time (12.20 CET) on Thursday.
Local media cited eyewitnesses as saying they saw emergency services rush to the scene, with "at least ten ambulances" along with police and fire crews.
"A rescue operation was subsequently led by the fire service, involving five appliances and two turntable crews," police said in a statement.
A full investigation has also be launched into the incident.
At a press conference, Chief Inspector Mark Runacres of Avon and Somerset Police confirmed three employees of Wessex Water and one contractor had been killed in the incident.
"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. This includes three employees of Wessex Water and one contractor," he said.
"Specially trained officers have this afternoon made contact with each of the families of those individuals and informed them of the sad news.
"This is a tragic incident and our thoughts and sympathies go out to them."
Authorities have set up a cordon around the blast site and have advised members of the public to avoid the area to allow the emergency services to carry out their work.
A spokesman for South Western Ambulance Service has also said that it sent "multiple resources to the scene", including land air and other specialist paramedic teams.
UK prime minister Boris Johnson said that he was "saddened" to hear of the deaths of those involved in the incident.
In a post on Twitter, he wrote: "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."