Three people were killed and several others were missing after a "devastating" explosion on Saturday flattened a low-rise apartment block in Jersey, authorities said.

Chief Minister Kristina Moore confirmed at least three fatalities, after a suspected gas leak around 4:00 am (0400 GMT) in the Channel island's port capital St Helier.

Security camera footage showed a fireball engulfing the three-storey, bayside building followed by thick smoke.

Nearby resident Anthony Abbott said his flat's windows were smashed inward by the blast wave, "and there was fire everywhere outside".

"It was very, very distressing," he told the BBC. "I'm a little bit shocked, but we are lucky we're OK."

Jersey's gas supplier, Island Energy, said it was working with the fire service to understand what happened.

The fire was put out but emergency services were conducting "significant work" at the scene, and the rescue operation could take days, police said.

Fire crews mobilised after residents reported smelling gas, Jersey police chief Robin Smith told reporters.

"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."

Prior to the updated death toll given by the chief minister, Smith said "around a dozen" people were missing, "but you will appreciate also that number could fluctuate".

Two others were taken to hospital, Smith said, describing them as "walking wounded".

"Specialist resources" have been mobilised to find anyone trapped in the rubble, according to the police, helped by an urban search-and-rescue team from southern England.

Tragic week

Moore expressed condolences and said residents displaced by the blast were being found somewhere to stay.

"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," she said.

The incident caps a tragic week for Jersey, a British Crown dependency not part of the United Kingdom, whose economy relies on banking, tourism and fishing.

The coastguard Friday abandoned a search for three Jersey fishermen missing for nearly 36 hours after their boat hit a freight ship and sank.

Skipper Michael Michieli and two crew members went missing early Thursday when their 18-metre (60-foot) wooden vessel collided with the Commodore Goodwill off Jersey.

The Commodore Goodwill is owned by Condor Ferries, whose Jersey offices lie near the destroyed apartment block.