Fear of possible coronavirus infections on a cruise ship carrying about 3,700 people became reality Wednesday as 10 of 31 passengers tested were confirmed to have positive results, fueling unease among officials that the number could go much higher.

The outcome was based on the results available after 273 people aboard the vessel were examined, health minister Katsunobu Kato said Wednesday morning. The 10 disembarked the Diamond Princess, which is docked at Yokohama port, and were taken to four hospitals in Kanagawa Prefecture.

The development suggests more passengers and crew members on the cruise ship could be infected and may not know it — at least four asymptomatic cases have been reported in Japan. Remaining passengers and crew will be confined to the ship for at least two weeks, Kato confirmed.