<p>Four people died on Thursday when a chemical tank exploded at a wastewater treatment plant near Bristol in western England, police said.</p>.<p>A fifth person was wounded in the explosion at the plant in Avonmouth, but their injuries were said to not be life-threatening.</p>.<p>Police said they would not be speculating on the cause of the blast but added it was not being treated as terror-related.</p>.<p>Avon and Somerset Police Chief Inspector Mark Runacres said that the explosion at the plant operated by Wessex Water occurred in a silo that holds treated bio-solids before they are recycled as organic soil conditioners.</p>.<p>Witness Jawad Burhan said there was a "helicopter looking for missing people" and that police closed a nearby road leading up to the plant.</p>.<p>"I heard the sound, I'm working beside the building in another warehouse. After 10 minutes I saw the helicopter coming and the police," he said.</p>.<p>Emergency services were called to reports of a large explosion at approximately 11:20 am (1120 GMT), with fire services leading the rescue operation.</p>.<p>Luke Gazzard, from Avon Fire and Rescue Service, said the incident had been "very challenging".</p>.<p>"Luckily our local fire station is not too far from here so we had crews in attendance very, very quickly," he said. "It is a terribly sad incident."</p>.<p>Police said three of the victims were employees of Wessex Water, while the fourth was a contractor.</p>.<p>Prime Minister Boris Johnson tweeted that he was "deeply saddened to learn that four people have lost their lives".</p>.<p>"Our hearts go out to the victims and their families," he added.</p>.<p>Another witness, Kieran Jenkins, told the BBC he was in a nearby warehouse when the explosion occurred, saying it was "shaking and we literally stood there in shock.</p>.<p>"Next thing you know we looked out of the windows and all we could see was people running.</p>.<p>"We don't know what happened. It was a bit of a shock really. I heard a bang... we didn't know what was going on," he added.</p>.<p>Police reassured local residents that there was "not believed to be any ongoing public safety concerns" following the blast but urged members of the public to avoid the area.</p>.<p>Local MP Darren Jones tweeted: "I'm pleased that the situation has been contained and that there is no further risk to local people".</p>.<p>"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," he added.</p>.<p>A probe has been launched into the blast with the Health and Safety Executive.</p>
<p>Four people died on Thursday when a chemical tank exploded at a wastewater treatment plant near Bristol in western England, police said.</p>.<p>A fifth person was wounded in the explosion at the plant in Avonmouth, but their injuries were said to not be life-threatening.</p>.<p>Police said they would not be speculating on the cause of the blast but added it was not being treated as terror-related.</p>.<p>Avon and Somerset Police Chief Inspector Mark Runacres said that the explosion at the plant operated by Wessex Water occurred in a silo that holds treated bio-solids before they are recycled as organic soil conditioners.</p>.<p>Witness Jawad Burhan said there was a "helicopter looking for missing people" and that police closed a nearby road leading up to the plant.</p>.<p>"I heard the sound, I'm working beside the building in another warehouse. After 10 minutes I saw the helicopter coming and the police," he said.</p>.<p>Emergency services were called to reports of a large explosion at approximately 11:20 am (1120 GMT), with fire services leading the rescue operation.</p>.<p>Luke Gazzard, from Avon Fire and Rescue Service, said the incident had been "very challenging".</p>.<p>"Luckily our local fire station is not too far from here so we had crews in attendance very, very quickly," he said. "It is a terribly sad incident."</p>.<p>Police said three of the victims were employees of Wessex Water, while the fourth was a contractor.</p>.<p>Prime Minister Boris Johnson tweeted that he was "deeply saddened to learn that four people have lost their lives".</p>.<p>"Our hearts go out to the victims and their families," he added.</p>.<p>Another witness, Kieran Jenkins, told the BBC he was in a nearby warehouse when the explosion occurred, saying it was "shaking and we literally stood there in shock.</p>.<p>"Next thing you know we looked out of the windows and all we could see was people running.</p>.<p>"We don't know what happened. It was a bit of a shock really. I heard a bang... we didn't know what was going on," he added.</p>.<p>Police reassured local residents that there was "not believed to be any ongoing public safety concerns" following the blast but urged members of the public to avoid the area.</p>.<p>Local MP Darren Jones tweeted: "I'm pleased that the situation has been contained and that there is no further risk to local people".</p>.<p>"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," he added.</p>.<p>A probe has been launched into the blast with the Health and Safety Executive.</p>