French fishing boats protest in front of the port of Saint Helier off the British island of Jersey to draw attention to what they see as unfair restrictions on their ability to fish in UK waters after Brexit, on Thursday amid fresh tensions between France and Britain over fishing. Photo: AFP

 Three people were killed and several others were missing after a "devastating" explosion on Saturday flattened a low-rise apartment block on the island of 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-story, 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 mobilized after residents reported smelling gas, Jersey police chief Robin Smith told reporters.

"We have a three-story building that has completely collapsed - described from a demolition point of view as a pancake that has dropped almost straight down," Smith 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."

AFP