Almost 500 passengers and crew became sick on a Royal Caribbean cruise, cutting short a seven-night cruise to the Caribbean.

The New York-listed cruise major said Thursday that 277 people had "experienced gastrointestinal illness, thought to be norovirus," CNN has reported.

That number jumped to 475 passengers and crew Saturday, prompting the 5,400-berth Oasis of the Seas (built 2009) to return to Port Canaveral, Florida, a day earlier than expected.

The Royal Caribbean International ship left the port 6 January on an itinerary that included stops in Haiti, Jamaica and Mexico with a return home today.

"As you may have heard from the captain's announcement, we have unfortunately experienced an increase in guests who have reported gastrointestinal symptoms," company officials said in a letter reportedly sent to guests.

"We hoped to give you an amazing vacation this week and we are sorry we fell short."

Royal Caribbean said in the letter that all passengers will get full trip refunds and up to $200 per person for any domestic flight changes and $400 per person for international.

Passengers who choose to keep the same flight arrangements will receive $200 per person for an one-night hotel stay.

"We are sorry for this unfortunate circumstance," the company said.

An email to Royal Caribbean was not immediately returned.