Buses believed to carry the U.S. passengers of the cruise ship Diamond Princess, where dozens of passengers were tested positive for coronavirus, leave the Daikoku Pier Cruise Terminal in Yokohama, south of Tokyo, Japan, February 17, 2020. Buses carrying passengers from a virus-hit cruise, including Americans, were seen leaving the Japanese port of Yokohama early on Monday. REUTERS/Athit Perawongmetha

Buses believed to carry the U.S. passengers of the cruise ship Diamond Princess, where dozens of passengers were tested positive for coronavirus, leave at Daikoku Pier Cruise Terminal in Yokohama, south of Tokyo, Japan, February 17, 2020. American passengers were taken off the cruise liner late on Sunday (February 16) to fly home after being quarantined for two weeks off Japan, while China said the rate of new coronavirus cases had slowed, calling that proof its steps to fight the outbreak were working. REUTERS/Issei Kato

Buses believed to carry the U.S. passengers of the cruise ship Diamond Princess, where dozens of passengers were tested positive for coronavirus, leave at Daikoku Pier Cruise Terminal in Yokohama, south of Tokyo, Japan, February 17, 2020. An announcement on the tannoy aboard the Diamond Princess, where 3,700 passengers and crew have been held since Feb. 3, told Americans to get ready to disembark on Sunday evening for charter flights home. REUTERS/Issei Kato

A bus believed to carry the U.S. passengers of the cruise ship Diamond Princess, where dozens of passengers were tested positive for coronavirus, leaves the Daikoku Pier Cruise Terminal in Yokohama, south of Tokyo, Japan, February 17, 2020. Passengers wearing masks could later be seen waving through the windows of buses as they departed the Daikoku Pier Cruise Terminal in Yokohama, south of Tokyo. REUTERS/Athit Perawongmetha

Buses believed to carry the U.S. passengers of the cruise ship Diamond Princess, where dozens of passengers were tested positive for coronavirus, leave at Daikoku Pier Cruise Terminal in Yokohama, south of Tokyo, Japan, February 17, 2020. Buses carrying passengers from a virus-hit cruise, including Americans, were seen leaving the Japanese port of Yokohama early on Monday. REUTERS/Issei Kato

Buses believed to carry the U.S. passengers of the cruise ship Diamond Princess, where dozens of passengers were tested positive for coronavirus, leave at Daikoku Pier Cruise Terminal in Yokohama, south of Tokyo, Japan, February 17, 2020. American passengers were taken off the cruise liner late on Sunday (February 16) to fly home after being quarantined for two weeks off Japan, while China said the rate of new coronavirus cases had slowed, calling that proof its steps to fight the outbreak were working. REUTERS/Issei Kato