"There is widespread suspicion that virus testing is not being done so as to suppress the number of confirmed infections," lawmaker Hiroshi Kawauchi of the main opposition Constitutional Democratic Party of Japan (CDP) said in the Diet on Thursday (Feb 27).

"Shouldn't the policy be to expand testing, detect infections early and to control clusters?"

Mr Kato denied that the government had been suppressing tests or trying to reduce the number of infections arbitrarily.

The source of this allegation is a chart, cited in Japanese media this week and widely shared on social media, that showed that South Korea had tested 40,304 people in total as of 4pm on Tuesday, of whom 977 were positive.

But despite Japan's ability to test up to 3,800 people a day, the latest Health Ministry figures show that as of 12pm on Wednesday, Japan had tested just 1,890 people altogether, of whom 164 people were positive.

They exclude Chinese visitors who have tested positive in Japan, as well as the 3,711 people who were on board the Diamond Princess cruise liner.

Together with Diamond Princess patients, a total of 6,300 tests were done between Feb 18 and Monday, Mr Kato said on Wednesday.

CDP leader Yukio Edano said: "There are many people who say they cannot be tested although their fever continues. Resources are not being fully mobilised."

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Meanwhile, there have been seven deaths in Japan, comprising three domestic cases and four former passengers of the Diamond Princess.

Two of the three domestic cases - a woman in her 80s in Kanagawa and a man in his 80s in Hakodate in Hokkaido - were confirmed to have been suffering from Covid-19 only in the postmortem stage, raising questions if earlier medical intervention might have been possible, should the right diagnosis been made sooner.

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Experts are split over Japan's cautious approach.

While some say that it is necessary to avoid causing panic and overwhelming the medical system, others have urged the government to make full use of its testing capacity to assuage unease.

"At the very least, the government should make it possible for anyone with pneumonia symptoms to be tested for the coronavirus wherever they are. It also needs to speed up inclusion of these tests under the public health insurance system," the Mainichi daily said in an editorial on Thursday.

Still, Dr Norio Ohmagari, director of infectious diseases at the National Centre for Global Health and Medicine, said: "It's extremely difficult to distinguish between the common cold and Covid-19. If we try to test all the people who seem to have a common cold, it will be a disaster for hospitals.

"Many will just go for outpatient and (proper attention cannot be given) to sick patients who require intensive care."