The number of passengers and crew who fell ill aboard a Royal Caribbean cruise ship has climbed to more than 600.

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

A total of 595 passengers and 50 crew fell ill on board the ship, said CDC spokesman Bernadette Burden. The vessel was carrying 3,050 passengers and a crew of 1,165.

Among those sick with vomiting and diarrhoea were some of the onboard entertainers, which caused shows to be cancelled, passengers reportedly said.

Officials have yet to determine the cause of the illness, but Royal Caribbean says the symptoms resemble norovirus, which causes nausea, vomiting and diarrhoea.

Explorer of the Seas departed from Cape Liberty cruise port in Bayonne, New Jersey, a week ago and will cut its planned 10-day cruise short by two days, the cruise company said.

“After consultation between our medical team and representatives of the US Centres for Disease Control and Prevention, we think the right thing to do is to bring our guests home early, and use the extra time to sanitise the ship even more thoroughly,” Royal Caribbean said.

The cruise line said it believes the illnesses are consistent with norovirus, the highly contagious virus spread from an infected person, contaminated food or water, or by touching contaminated surfaces, according to the CDC.

“Disruptions caused by the early wave of illness means that we were unable to deliver the vacation our guests were expecting,” Royal Caribbean said.

The line plans to compensate passengers with a full refund as well as hotel and air fares.

Norovirus was responsible for widespread illness on seven cruise ships last year.