Passengers leaving quarantined cruise ship

Roughly 500 people left a cruise ship docked under quarantine in Japan on Wednesday after tests indicated that they had not contracted a new form of coronavirus that has sickened thousands in China and hundreds on board the vessel.

The Associated Press and Reuters reported that as many as 621 cases of the virus were reported on the Diamond Princess. Authorities have faced public criticism for keeping passengers and crew on board the ship in quarantine, which many said allowed the infection to spread.

Health officials in Japan have defended their handling of the outbreak, pointing to the large number of cases on board.

“Unfortunately, cases of infection have emerged, but we have to the extent possible taken appropriate steps to prevent serious cases, including sending infected people to hospital,” health minister Katsunobu Kato said at a parliamentary briefing, according to Reuters.

Wednesday marks the end of a two-week quarantine imposed by officials. Passengers, including at least 100 Americans, will have to wait a further two weeks before traveling to the U.S. under Centers for Disease Control and Prevention (CDC) guidelines.

The CDC said in a statement obtained by Reuters that the quarantine “may not have been sufficient to prevent transmission among individuals on the ship.”

Thousands of Chinese citizens and others have been infected in the outbreak that is believed to have originated at a seafood and live animal market in Wuhan, China, which has since been shuttered by authorities. Hundreds have died from the disease, which presents as a form of pneumonia, and a handful of cases have been reported in the U.S.