"This is one of the things I'm very worried about," said Koike on the sidelines of an opening ceremony for a 15,000-seat gymnasium in eastern Tokyo that will host volleyball and wheelchair basketball competitions this summer.
Japan on Saturday stepped up its response to the epidemic, classifying the coronavirus as a "designated infectious disease," allowing compulsory hospitalization and the use of public funds for treatment, among other measures.
Koike said she was now working with local and national authorities on how to monitor the virus and to implement measures against its spread to protect the city's residents.
"I would like you to wash your hands and fingers properly, and wear masks to protect yourselves. There are many ways to do it, but I'd like you to start yourselves with such small steps to control it," said Koike.
The outbreak originating in the Chinese city of Wuhan prompted organizers to cancel Olympics qualifying events slated to take place in China such as boxing and badminton.
"Countermeasures against infectious diseases constitute an important part of our plans to host a safe and secure games," Tokyo 2020 said in a statement responding to recent enquiries about the issue, pledging collaboration with authorities.
Casting a shadow over the opening was an announcement by the International Paralympic Committee (IPC), which on Friday said it could remove wheelchair basketball from the games if its global body does not improve its athlete classification process.
The IPC said the International Wheelchair Basketball Federation (IWBF) defined "eligible impairments" differently to the mandatory list agreed on by the IPC's general assembly.
"It's a very popular discipline," said Koike, calling on the parties involved to make an effort to resolve the impasse through discussions.
The Ariake Arena opening ceremony featured a presentation by Japan's volleyball and wheelchair basketball teams. It boasts rich wooden paneling and a concave roof to reduce indoor space to save on air conditioning and lightning.