FOUR people have died following a major explosion at a waste water treatment works near Bristol, police have confirmed.

A major incident was declared after the blast, with emergency services being called to Wessex Water's premises in Avonmouth just after 11.20am on Thursday.

Avon and Somerset Police have confirmed that three Wessex Water employees and one contractor had died, and their relatives have been informed.

Chief Inspector Mark Runacres told a press conference at the scene: “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.”

Mr Runacres added: "A fifth person was also injured but their injuries are not believed to be life-threatening.

"A thorough investigation will be carried out into what happened today, involving a number of agencies and the Health and Safety executive in due course, and we will not be speculating on the cause of the explosion while such work is being undertaken.

"I can confirm though that this is not being treated as a terror-related incident."

Prime minister Boris Johnson tweeted that he was "deeply saddened" by the news.