Four people have died following an explosion at a waste water treatment works.
A major incident was declared at Wessex Water's Bristol water recycling centre in Kings Weston Lane, Avonmouth, after reports of a "large explosion" earlier today.
Among those killed were three employees of Wessex Water and one contractor, Chief Inspector Mark Runacres, from Avon and Somerset Police, said.
Speaking at a press conference at the scene, he added: "Emergency services were called at approximately 11.20am to reports of a large explosion involving one of the chemical tanks at the site off Kings Weston Lane.
"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.
"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."
Prime Minister Boris Johnson said "our hearts go out" to the victims and their families.
"Deeply saddened to learn that four people have lost their lives in the water works explosion in Avonmouth," he said on Twitter.
"Our hearts go out to the victims and their families.
"Thank you to the emergency services who attended the scene."
Jawad Burhan took a photo showing a tank that had exploded after the blast.
He said there was a "helicopter looking for missing people" and police had closed a nearby road leading up to the building, which he believed was a waste centre.
"I heard the sound, I'm working beside the building in another warehouse," he said.
"After 10 minutes I saw the helicopter coming and the police."
Darren Jones, MP for Bristol North West, said: "This is a serious incident and my thoughts are with those workers who have injured on site today.
"I'm grateful to our fire, police and ambulance staff for their quick response."
