TOKYO - A surgeon and a patient at the same Wakayama hospital, near Osaka, have been infected with the coronavirus, officials said on Friday (Feb 14), with three other new cases surfacing in Tokyo and Okinawa.

These developments come a day after Japan reported its first coronavirus-related death - a woman in her 80s in Kanagawa prefecture, south of Tokyo.

Japan's 35th case is a female taxi driver in her 60s in Okinawa, who is suspected to have ferried passengers of the Diamond Princess cruise ship when they disembarked in the prefectural capital of Naha on Feb 1.

The country's 36th and 37th cases are both linked to an infected Tokyo taxi driver, who is the son-in-law of the elderly woman who died. The man, who is in his 70s, had attended a new year's gathering on board a 'yakatabune' boat cruise last month.

An employee of the yakatabune, as well as an employee of a taxi driver's union, were confirmed to have been infected on Friday.

Domestic media cited experts as wondering if a "stealth outbreak" might already be underway in Japan.

Tohoku University Professor Hitoshi Oshitani told Jiji Press that efforts should be devoted to reducing the speed of contagion and treating the severely ill, as an epidemic is "likely occurring to some extent".

None of the new cases have cited any recent overseas travel, let alone to Wuhan, the epicentre of the outbreak. This has left officials perplexed as to how an emerging bunch of cases around Tokyo and in Wakayama - which borders Osaka - have occurred.

In Wakayama, officials on Friday confirmed that a patient at the Saiseikai Arida Hospital was suffering from Covid-19, a day after they said a surgeon had been infected.

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The farmer, in his 70s, is in serious condition. But officials stressed that doctor-to-patient transmission was unlikely, as the farmer was not treated by the infected surgeon.

They raised the possibility that both men were infected outside hospital grounds.

At least three others at the hospital - a doctor and two another patients - have developed symptoms of pneumonia and are being tested for the coronavirus.

The surgeon, who is in his 50s, was on Thursday (Feb 13) confirmed to be suffering from Covid-19, first medical professional to be infected in Japan.

Authorities are conducting urgent contact tracing to see if he had contracted the coronavirus from a patient and how many others he might have passed it to.

He first developed a slight fever on Jan 31, but returned to work from Feb 3 to 5 after taking medicine to bring down his fever. He developed a 38 deg C fever last Saturday, and a CT scan revealed symptoms of pneumonia.

Health Minister Katsunobu Kato said the central government will send an infectious diseases expert to the Saiseikai Arida Hospital.

A day earlier, a woman in her 80s died in Kanagawa prefecture, south of Tokyo, but it was only during the post-mortem after her death that doctors found that she was infected with the coronavirus.

She first saw the doctor for lethargy on Jan 22, and was hospitalised for pneumonia on Feb 1.

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"The relationship between the coronavirus and the person's death is still unclear," Health Minister Katsunobu Kato said. "Testing was conducted because she was suspected of being infected with the coronavirus. Her positive result was confirmed only after her death."

This is the third coronavirus death outside mainland China, with Hong Kong and the Philippines having earlier reported one each.

Japan also confirmed two other new cases on Thursday: the taxi driver in Tokyo as well as a company employee in his 20s in Chiba, to the east of the capital.

Nothing has been found to connect the Chiba man to any of the existing cases.

These new diagnoses indicate human-to-human transmission of the disease within Japan's borders although the Health Ministry said on Thursday that there was still no evidence of any community spread.

Separately, another 218 people have tested positive for the new coronavirus on board the Diamond Princess cruise liner, which has been quarantined off Yokohama since Feb 5.

This is nearly 6 per cent of the 3,711 people on the ship manifest, with the cases traced to a Hong Kong man who disembarked on Jan 25.

Ten are in serious condition, of whom eight are Covid-19 patients.

The authorities said on Thursday that passengers aged 80 and above who either have pre-existing illnesses or are staying in cabins without windows will be allowed to move off the ship to government-designated lodgings for the rest of the quarantine period, which ends next Wednesday (Feb 19).

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"There are some people whose health may deteriorate by staying aboard for an extended period," Mr Kato said on Thursday.

Japanese Prime Minister Shinzo Abe has pledged to devote 15.3 billion yen (S$193.5 million) in emergency measures to fight the virus and to ensure that 600 million new masks will be available within a month.

He had earlier vowed to raise the testing capacity for the new coronavirus from 300 cases a day to more than 1,000 by next week.

Japan will send a fifth chartered flight to Wuhan on Sunday, Foreign Minister Toshimitsu Motegi said, to bring home stranded Japanese nationals and their Chinese spouses. Thus far, Japan has evacuated a total of 763 people.