French authorities on Wednesday allowed asymptomatic passengers to leave a British cruise ship, saying a gastrointestinal virus was behind an outbreak of sickness that came after an elderly man died of a heart attack.

Earlier on Wednesday, authorities had ordered a lockdown for the over 1,700 passengers and crew on the vessel, but insisted there was no connection with the hantavirus outbreak suspected of killing three people on the Dutch-flagged MV Hondius cruise ship.

Testing confirmed that the outbreak on the Ambition, a cruise ship anchored in the port of Bordeaux, in western France, was "a gastro-intestinal infection of viral origin," the local government and regional health agency said in a statement.

They said there were no severe cases, and that asymptomatic individuals were now free to disembark, but that those infected were required to remain in isolation on board.

News that a 92-year-old British passenger had died on the ship as dozens of other passengers suffered upset stomachs initially caused concern. But health authorities said the man had suffered a heart attack and that his death appeared unrelated to the illness.