Almost 500 passengers have been hit with gastro aboard a Royal Caribbean ship after the vessel departed Port Canaveral in Florida.

Initially, 277 passengers had fallen ill when Oasis of the Seas departed on Sunday, and number of sick people has increased to 500.

The cruise, which was to sail around the Caribbean, has been cut short and the ship will dock back at Port Canaveral on Saturday. The line announced it would be refunding all passengers onboard, due to the outbreak according to NBC News.

Passenger Shawn Popeleski told the Orlando Sentinel that they were told the outbreak is “most likely norovirus.”

Norovirus is highly contagious and people usually fall sick by consuming contaminated food or water or by touching contaminated surfaces.

Symptoms include stomach pain, nausea and diarrhea.