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People reported hearing a loud bang and smoke could be seen coming from the area
One person has died after an explosion at a block of flats in Jersey.
About a dozen people are missing and two are being treated in hospital after the explosion on Pier Road in St Helier just before 04:00 GMT.
Searches are under way and Chief of Police Robin Smith said he expected it to take "a number of days".
"It is a pretty devastating scene… the scene is a very dangerous one for all of our staff," he said.
He said: "I don't know the exact number of the flats destroyed, but we have a three-storey building that has completely collapsed.
"Described as, from a demolition point of view, probably as a pancake that has just dropped almost sort of straight down."
Mr Smith confirmed the fire service had attended the scene on Friday night after the smell of gas was reported.
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Chief of Police Robin Smith: "It is a pretty devastating scene"
Emergency services said a fire caused by the explosion had been extinguished and the police force said it was using specialist resources to find "anybody trapped in the rubble".
However, Jersey Fire & Rescue said "pockets of fire" had been discovered in the area.
It confirmed that the South West Hazardous Area Response Team had arrived in the island, alongside an Urban Search and Rescue Team from Hampshire & Isle of Wight Fire & Rescue Service.
A Chinook helicopter, typically used for military operations, was expected to land at Jersey airport at about 16:00 GMT with specialist equipment on board, the Government of Jersey said.
Anthony Abbott told the BBC how the flat he shares with his wife had been severely damaged by the explosion.
"We heard an explosion at about four o'clock this morning, we got up and we found it [debris] in the flat, all the windows had been put in, the staircase had been damaged and there was fire everywhere outside," he said.
"It was very, very distressing.
"There was young children in the flat, we helped them out and we got them down… the housing and everyone's been very good to us at the moment… helping us."
Mr Abbott added: "I'm a little bit shocked but we are lucky we're OK."
Another resident described being woken up by what she thought was an earthquake at about 03:50.
"The bed started to shake and there was this massive bang," she said.
"I checked online for news about an earthquake or lightning, I had no idea what it was."
Luis, who was rescued from his flat with his nephew, said his doors and windows had been "blown off" by the explosion.
He said he felt "pretty shaken up but OK, it's traumatising".
Daniel Hunt, 19, from St Helier, tweeted pictures of the fire from his flat.
He said: "Everything shook, my windows were shaking, the whole room shook.
"You could feel the shockwave through your bedroom almost.
"In the moment you think, what was that?"
The government has repurposed its Covid helpline for those who need support following the incident.
BBC Jersey reporter Chris Craddock, who was near the scene earlier, said: "You could see glass, you could see rocks, you could see stones strewn across the area both on the pavement and on the road.
"Police have cordoned off the area and are diverting traffic."
Chief Minister Kristina Moore said the island had seen "what amazing strength we have within our emergency services", with 21 police officers, nine paramedics and 19 firefighters deployed to the scene.
"I wanted to offer my heartfelt thanks this morning to all of the emergency services who have attended," she said.
"Everybody wants to help, we're really grateful for support."
Ms Moore said it had already been "a difficult week for islanders", after the captain and two crew members of a fishing boat went missing following a collision with a Condor ferry on Thursday.
The Government of Jersey has asked islanders not to go to the Emergency Department "unless absolutely necessary".
About 20 to 30 people were being cared for at St Helier Town Hall which was closed later with people accommodated elsewhere, the parish authority said.
The States owned housing company Andium Homes is responsible for the flats, and said its "focus at the moment is on supporting our residents on that estate".
Island Energy said it was working with the fire service to "understand exactly what has happened".
"We are co-operating fully with the emergency services following the serious incident in St Helier this morning," it said.
"Our thoughts are with the residents of the area and anyone who has been affected."
The town church will be open from 17:00 GMT for islanders to light candles and pay their respects.
The Bailiff of Jersey, Sir Timothy Le Cocq, said the island's response to recent events had been honourable.
"My thoughts at this time are with all involved, either those who have suffered loss or those working so hard since the early hours to help those affected.
"But, in particular, with the families who are waiting for information on family members who are unaccounted for," he said.
Jersey Bulls FC held a minute's silence before the team's match against Horley, marking the "terrible tragedies" which had taken place in Jersey during the week.
Pier Road, Pier Road car park and South Hill have all been cordoned off and the police have asked people to avoid the area.
Meanwhile Fort Regent is also closed.
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One killed in explosion at flats in Jersey – BBC
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