At any given time, seven out of eight beds in the intensive care unit of St. Luke's International Hospital in Tokyo are taken up by critically ill coronavirus patients.

"If we max out eight beds, we can't place patients who suddenly take a turn for the worse, so we always keep one bed open," said Fumie Sakamoto, who manages the 500-room hospital's infection control division.

The extra ICU bed also needs to stay open for any coronavirus patients who could arrive at any hour of the day in an ambulance, Sakamoto said.