The U.S. Centers for Disease Control and Prevention say 281 passengers and 22 crew members have fallen ill aboard the Royal Caribbean cruise ship Explorer of the Seas.
A total of 3,050 passengers and 1,165 crew members are aboard.
The CDC said it's not yet clear what is causing the illness.
Health officials will board the ship on Sunday while it's docked in St. Thomas in the U.S. Virgin Islands.
Authorities said specimens are being collected and will be tested.