A lifeboat has fallen from its moorings aboard the world's largest luxury liner, Harmony of the Seas, killing one person and injuring four.

The ship was docked at the French Mediterranean port of Marseilles at the time, emergency services have told media.

French fire and rescue services say the dead and injured were aboard the lifeboat at the time of the accident.

"One person is dead and four are injured, including two whose lives are in danger," a fire department spokesperson has told AFP.

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There was no immediate confirmation of local media reports that they had been taking part in a safety drill at the time.

It is understood all are members of the ship's crew and La Provence is reporting the dead person is a Filipino aged 42 years.

The 120,000-tonne liner operated by Florida-based Royal Caribbean only entered service in May.

At 66m, it is the widest cruise ship ever built, and its 362m length makes it 50m longer than the height of the Eiffel Tower. It has 16 decks and can carry more than 6000 passengers and 2400 crew.