Updated: Dec 9, 2020
Four people have died and another has been injured in a large explosion at a waste water treatment works.
A witness to the aftermath of the Avonmouth explosion described hearing a "boom and echo" which shook the ground.
"It was quite short-lived, I'd say about two or three seconds. Sort of a boom and echo and then it just went quiet," he said.
Firefighters were called to Wessex Water's premises at about 11:20 GMT.
The blast happened in a silo containing treated biosolids and was not terror related, police said.
The police have declared a major incident and are investigating the circumstances of the blast.
The families involved have been informed and are being supported by officers.
Colin Skellett, chief executive of Wessex Water, said the company's "thoughts are with the families, friends and colleagues of those involved".
He said they were "absolutely devastated that the tragic incident at our site earlier today has resulted in four fatalities".
The company is working with the Health and Safety Executive as part of the investigation.
Luke Gazzard, Avon Fire and Rescue Incident Commander, said the incident had been "very challenging".
The blast is not being treated as terror-related and involved one of the chemical tanks, Chief Inspector Mark Runacres, from Avon and Somerset Police, said.
Prime Minister Boris Johnson said in a tweet he was "deeply saddened" to learn of the loss of life in the explosion.
"Our hearts go out to the victims and their families. Thank you to the emergency services who attended the scene," he said.
Labour leader Keir Starmer said: "My thoughts are with all those who tragically lost their lives today in Avonmouth. My heart goes out to their friends and family.
"Thank you to our emergency services for all their work."
Darren Jones, MP for Bristol North West, tweeted: "My family and I are keeping those affected in our thoughts and prayers, following the tragic consequences of the explosion in Avonmouth today.
"Can I thank the emergency services - including Avon and Somerset Police, the South West Ambulance Service and Avon Fire & Rescue - for their responsiveness and support.
"I'm pleased that the situation has been contained and that there is no further risk to local people.
"There will be a full investigation taking place but, for now, we pay our respects to those who have suffered and lost their lives today."
Biosolids are "treated sludge", a by-product of the sewage treatment process.
According to Wessex Water, the sludge is treated in anaerobic digesters, oxygen-free tanks, to produce agricultural fertiliser and renewable energy.
People have been urged to stay away from the area.