At least three people have died and about 12 people are believed to be missing after an explosion in a block of flats in St Helier, Jersey police have said. The blast at Haut du Mont, Pier Road, in the capital, occurred at about 4am on Saturday, less than eight hours after firefighters had been called to the site after concerns from residents, it was confirmed. Two people who were in hospital earlier have been discharged and one other person is receiving treatment for non-serious injuries. In a press conference on Saturday afternoon alongside the head of the fire, police and ambulance services, the island’s chief minister Kristina Moore announced at least three people had died, with a search and rescue operation to find more people still taking place – which was expected to continue throughout Saturday night. She added it was an “unimaginable tragedy” for the Channel Island. Robin Smith, the chief officer of the States of Jersey police, said the scene was one of “complete devastation”. Police said the site remained “highly unsafe” with “pockets of fire” discovered hours after the “very, very significant” explosion. Paul Brown, chief fire officer, added: “The primary challenge is the fact that we have a dangerous structure that has collapsed … anything that we do, or do in the wrong way, may then jeopardise the chance of survival of anyone who might be rescued.” The operation will continue “for days, maybe weeks”, Smith said, and added that it was “important to have resources to continue to keep going”. Brown also revealed firefighters were called to the scene at 8.36pm on Friday, and an investigation was carried out. Asked if this had anything to do with the explosion, he said: “I can confirm that the fire and rescue service did attend. “I don’t know the exact number of firefighters, but they did attend. The call was received at 20.36 yesterday evening. “I know that they did conduct investigations, but I think at the moment what I’m focused on is just the emergency response. “I will give you an answer to that but what I’d like to do for the moment is focus on the emergency response, talk to my colleagues and consider those bits that are subject to investigation – and make sure I don’t tell you something that I need to tell someone else first.” Smith said it would not be helpful to speculate about what happened at this stage. The cause of the explosion remains unknown. Smith had earlier said there could be more deaths. “We have a three-storey building that has completely collapsed – described from a demolition point of view as a pancake that has dropped almost straight down,” he said. “There is also damage to a nearby building as well, another block of flats that the fire service needs to make safe. It is a pretty devastating scene, I regret to say.” The force had said earlier that relatives were being contacted by family liaison officers. Daniel Hunt, 19, who lives across the bay, said the explosion woke him at about 4am and he saw the building in flames. “My bedroom was shaken from the explosion, with the windows rattling, which was all very unnerving,” he said. “I went outside to take a look … I could see what looked like police and firefighters shining torches through windows of surrounding buildings, I assume as they were evacuating the surrounding area.” Smith said police would investigate the possibility of safety issues regarding the gas supply. Island Energy, the gas supplier to the building, said it was working with the fire service to “understand exactly what has happened”.