The team says it was found in recent days that young people with minor symptoms are thought to play a major role in transmitting the virus unknowingly at locations where people gather.

It says about 80 percent of the infected people do not spread the virus. But it listed cases in which a single carrier infected multiple people through close contact in closed spaces such as live music concerts, sports gyms and restaurants that offer buffets.

The team analyzed the situation in the northern prefecture of Hokkaido which has the largest number of cases in Japan. The team found that there was a high risk of contagion in urban areas where socially and economically active people tend to gather.

The team says avoiding such crowded places in the next two weeks can help contain the outbreak.

The experts urge people to refrain from going out if they have mild symptoms of the common cold, to avoid events held in places with poor ventilation, or where people communicate with each other in close quarters.

The team says infection risk will be low if people instead go outdoors for a walk or activities that involve little contact with others. They advise talking to other people at arm's length.

The team says people aged between 10 and 39 may spread the virus to people who have a high risk of getting seriously ill. It says young people can help protect the lives of vulnerable people by avoiding crowded places with poor ventilation.