Just days after releasing nearly 1,000 passengers from the cruise ship quarantined for two weeks in the port of Yokohama that has been a coronavirus hot spot, Japan’s health minister admitted that 23 passengers had been mistakenly cleared to leave without taking a valid recent test.

In a news briefing on Saturday night, the health minister, Katsunobu Kato, apologized for the error that allowed the passengers, who had not been tested since before the ship went into lockdown on Feb. 5, to leave the Diamond Princess.

The Japanese Health Ministry said it had tested them and checked for symptoms, and certified that they posed “no risk of infection.”

Mr. Kato said that all 23 mistakenly cleared passengers had boarded some form of public transportation after disembarking. He said none of them had reported any symptoms so far and 20 had already agreed to be retested, with three negative tests so far.

Although several governments that evacuated citizens from the ship — including those in the United States, Australia, Hong Kong and South Korea — confined them for an additional 14 days at home, Japan said that passengers who had tested negative for coronavirus and showed no symptoms could leave starting this week.

On the subject of the passengers released untested, Mr. Kato said that public health officers who had been conducting the tests missed the 23 passengers as they went door to door.

“While they made their multiple rounds to take samples, some passengers left their rooms to go outside and do exercise or something,” he said, “so they were unavailable.”