At least one of every two instances of human-to-human transmission of the new coronavirus is believed to occur while the first patient is not yet showing symptoms, according to an Japanese university research estimate.

Based on its determination, the team headed by Hokkaido University professor Hiroshi Nishiura has called for taking preventive measures and reinforcing the medical system for a potential spike in coronavirus patients, rather than focusing exclusively on isolation to contain the disease.

According to their estimate, based on data from 26 human-to-human infections released by six countries including China, Thailand and the United States, the timing of the secondary infection is shorter than previously thought.

Although the average incubation period is believed to be about five days, the researchers found that secondary patients in more than half of the 26 human-to-human cases under study developed pneumonia symptoms within five days.

The team concluded that these secondary patients were infected during the incubation period for the first patients.

"The findings suggest that it is difficult to contain the illness simply by isolation," Nishiura said. "We need to put more emphasis on preventing the infection of people at high risk, such as the elderly."

"It is also important to prepare the medical care system so that we will not experience confusion even in the event of a greater number of pneumonia patients," he added.

The number of people who have caught the new coronavirus in mainland China, where the outbreak began, has topped 31,000, with the death toll now beyond 700, according to the Chinese government.

Many countries are struggling to contain the outbreak by quarantining infected patients.