Shortly before 11 a.m., they began making their way off the ship through an improvised tunnel shrouded in blue tarp, through an array of orange pylons and out into a parking lot under a clear sky.

Taxis may have been in short supply, but the news media was not.

One of the earliest to disembark, a woman wearing a conical rice hat and a heavy-duty face mask with a strap hanging loose, was mobbed by journalists as she walked out of a guarded gate, pulling a red suitcase. She eventually wandered off on foot.

One passenger, Masako Ishida, 61, remained on board on Wednesday as she waited to receive her test results, and said she was frustrated by the suggestion that anyone who tested negative should have to remain in quarantine any longer.

“I heard that some people think us passengers should be put another two weeks in quarantine,” she said. “We were quarantined, and if we test negative, we will be given a certification that proves we’re negative. We’re one of the safest people right now.”

Another passenger seemed less certain.

“I’m a bit concerned if I’m OK to get off the ship, but it was getting very difficult physically, a 77-year-old man who got off with his wife told the Kyodo News agency. “For now, we just want to celebrate.”

Dr. Iwata, the infectious disease expert, sounded far more concerned.

He said he had visited the ship on Tuesday with the goal of advising public health officials on how to prevent the further spread of infection. He expressed astonishment at what he had seen, and took to YouTube to share his findings.

Health ministry officials, crew members and psychiatrists mingled and ate together, Dr. Iwata said, with some in full protective gear and others not — a violation of ordinary procedures.