Police reported last month the deaths of 11 people deemed to be unnatural before tests showed the victims had been infected with the coronavirus, media outlets reported Tuesday.
Japan, with more than 260 virus-related deaths, has avoided the kind of explosive outbreak that has plagued the United States and many European nations, raising questions over whether testing here has been sufficient.
Some of the 11 died at home and one was found lying in a street, the Nikkei financial newspaper and other media said, citing the National Police Agency.
Six were in Tokyo, where virus cases have topped 3,000, from a nationwide tally of 11,157.
Contacted by Reuters, the NPA said it could not confirm the facts before receiving questions by fax.
One of the cases police reported in the month to mid-April involved a man in his 60s found on a street in eastern Tokyo and taken to hospital, the Nikkei said.
A PCR test after he died from symptoms of pneumonia confirmed that he had been infected, it added.
The government has said it follows World Health Organization guidelines for virus testing, with all suspicious pneumonia deaths tested for the respiratory disease caused by the virus.