BAYONNE, N.J. (TheBlaze/AP) — The number of passengers and crew reported stricken ill on a cruise ship returning to New Jersey has risen to nearly 700.

The U.S. Centers for Disease Control and Prevention said Wednesday its latest count puts the number of those sick aboard the Explorer of the Seas at 630 passengers and 54 crew members. On Sunday, estimates were only in the 300s, showing just how quickly a virus in a confined space can spread.

Caribbean Cruise Ship Outbreak

The Royal Caribbean International’s Explorer of the Seas is docked at Charlotte Amalie Harbor in St. Thomas, U. S. Virgin Islands, Sunday, Jan. 26, 2014. U.S. health officials have boarded the cruise liner to investigate an illness outbreak that has stricken at least 300 people with gastrointestinal symptoms including vomiting and diarrhea. (AP/Thomas Layer)

Royal Caribbean said most guests who fell ill are now up and about as the ship heads to port in Bayonne, where it is scheduled to dock Wednesday afternoon.

The CDC is recommending that people who still have symptoms be housed in nearby hotels or seen at medical facilities.

Health investigators suspect a norovirus is to blame. If it is, the CDC said it would be one of the worst cruise ship norovirus outbreaks in 20 years.

The ship had to cut short a 10-day cruise after more than 600 passengers and crew members experienced vomiting and diarrhea.

Royal Caribbean is providing all guests a 50 percent refund of their cruise fares and an additional 50 percent future cruise credit. It’s also reimbursing airline change fees and accommodations for guests who had to change plans for traveling home.

Guests stricken with the illness were were confined to their staterooms, but they are also being provided a credit of one future cruise day for each day of confinement.

After returning to port, the ship will undergo a third sanitation and no one will be allowed aboard for a period of more than 24 hours as an extra precaution, the cruise line said.

Explorer of the Seas is on track to depart at its originally scheduled time Friday afternoon on its next cruise, a 9-night trip with port calls in Puerto Rico, St. Thomas, Dominican Republic and Haiti, a Royal Caribbean spokeswoman said.

A news release from the company assured guests that they “can be confident that all possible measures will have been taken to prevent further problems.”