The number of passengers and crew who fell ill aboard a Royal Caribbean cruise ship climbed to more than 600 on Monday, many of them vomiting and suffering diarrhea.

The updated sick count aboard the Explorer of the Seas, which cut short its Caribbean cruise and was expected to dock in New Jersey on Wednesday, is more than double the 300 originally thought to have been felled by gastrointestinal illness, according to the US Centers for Disease Control and Prevention.

Among those sick were some of the onboard entertainers, which caused shows to be canceled, passengers said.

"I started with upset stomach and vomiting, and that lasted all night and into the morning," passenger Joseph Angelillo told CNN in a telephone interview.

Altogether, 595 passengers and 50 crew members fell ill aboard the ship, CDC spokeswoman Bernadette Burden said. The ship was carrying 3,050 passengers and a crew of 1,165.

The ship departed Cape Liberty Cruise Port in Bayonne, New Jersey, on January 21 and will cut its planned 10-day cruise short by two days, returning to its home port on Wednesday, the cruise company said.

The CDC said Monday the cause of the sickness was unknown but that an environmental safety officer and an epidemiologist boarded the ship on Sunday in St Thomas in the US Virgin Islands to determine the cause of the outbreak and the proper response. - Reuters