Two Irish citizens who were on board the Diamond Princess cruise ship have been diagnosed with the new coronavirus.
They were among 15 citizens trapped on board two virus-stricken luxury cruise ships at the centre of a quarantine alert.
The pair - who live in Germany - are now being treated in a Tokyo hospital after contracting the virus while in isolation on one of the liners.
The news came as it emerged that two more Irish citizens who were on board another cruise ship, locked in quarantine amid a coronavirus scare, flew home last weekend without being screened.
The pair were holidaying on the Westerdam cruise ship, which is now docked indefinitely off the Cambodian coast.
Seven other Irish people are being tested for the virus, along with other passengers and crew, in Cambodia.
The ship had been stuck at sea for days after Japan, the Philippines and Thailand turned it away over concerns that it had passengers who could have been infected.
Last Friday Cambodia finally let it dock and some passengers were allowed to leave.
However, on Saturday an 83-year-old American passenger tested positive for the coronavirus during a stopover in Malaysia on her way home.
Now questions are being raised over how the woman was infected.
About half of the more than 2,500 passengers have already left the ship.
The Herald has established that by the time the woman was diagnosed, two citizens were already travelling home.
Sources said they have followed all health protocols since landing back in the country - and Ireland remains free of the virus. Of the seven other Irish on board the ship, only two are normally resident in this country.
A total of 13 Irish citizens have been trapped on board the two coronavirus-stricken luxury cruise ships.
Some nine other Irish were passengers on the Westerdam cruise ship, off the coast of Cambodia, which was also struck by the coronavirus.
Seven of these remain in Cambodia and are being screened for the virus, along with other passengers and crew.
Foreign Affairs officials said they are liaising with the two groups and hope to arrange transport for them out of Japan and Cambodia if they want to leave.
Nearly 3,000 people are still on board the Diamond Princess and were originally told their 14-day quarantine would end today.
It was planned for disembarkation to begin at around 10.30am local time - but Japanese Health Minister Katsunobu Kato said the process of leaving the ship could last two to three days. A couple from Co Meath were still on the Diamond Princess yesterday, along with two Irish crew members.
Tanaiste and Foreign Affairs Minister Simon Coveney said the two Irish citizens who tested positive for the virus are "being treated in hospital in Japan".
"These citizens share dual citizenship with another EU member state and are not normally resident in Ireland," he said.
"Our embassy in Tokyo is in ongoing contact with them regarding their consular needs.
"We are also in close contact with those who remain in quarantine on the ship.
"We are working with our EU partners and other like-minded countries regarding options for their return."
The Westerdam Cruise Ship is currently docked off Sihanoukville, Cambodia and some of the Irish passengers are ashore in a hotel.
Mr Coveney added: "Seven are currently being screened, along with other passengers and crew."