While some Americans aboard the Diamond Princess cruise ship, quarantined in Yokohama port, left Monday on chartered flights back home, others opted to stay.

One passenger who chose to remain was Matthew Smith, who said he felt an "about-face" by the U.S. government risks undermining the quarantine program put in place by Japan.

Based on the seating capacity of buses that transported passengers wishing to leave, Smith estimated there were still roughly 50 to 60 Americans still on the vessel. The Japan Times could not independently confirm the number.