A three-storey block of flats has been completely obliterated on the island of Jersey in an explosion so huge it was picked up on British earthquake monitors.

Three people are confirmed dead and as many as 12 could be missing, with police saying it could take weeks to search the rubble.

The horror explosion and fire happened near the harbour in the capital St Helier early on Saturday morning (0400 GMT) while people were sleeping.

Neighbours reported their own homes shaking and being thrown from their beds as debris was projected from the explosion.

Chief of Police Robin Smith described a blast scene of “complete devastation” on Pier Road.

He would not speculate about what happened but said authorities had  “working hypotheses”.

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Smith confirmed fire services had been called to the property on Friday before the explosion after residents had reported the smell of gas.

He said 20 to 30 people had been evacuated and there were two “walking wounded” receiving hospital treatment.

Asked about the possibility of more fatalities he said: “There has to be a recognition that we could have more fatalities.

“This is a protracted incident which is going to go on for days, maybe weeks.”

Jersey is a British Crown Dependency with a resident population of more than 100,000 people, located off the coast of northern France.

The explosion and fire can be seen from across the harbour. Photo: Daniel Hunt/PA Wire

Chief Minister of Jersey Kristina Moore said it was a “huge shock” and “our condolences go to the families who are affected”.

“Through these difficult times, I think it’s reassuring for everyone to see what amazing strength we have within our emergency services and, again, we just thank everybody who stepped up and came to the rescue and continue to work on the scene.

“This is going to take some days and we will keep everyone updated and fully informed and we will do our very best to ensure everybody is properly looked after.”

Jersey Consumer Council Chairman Carl Walker said: “Thoughts are with all those affected by this morning’s explosion in St Helier, which was powerful enough to be picked up on British Geological Survey’s earthquake monitors.

“It’s now time for Jersey’s community to respond like never before.”