Dr Frank Atherton, the chief medical officer of Wales, said the patient who had tested positive for coronavirus (Covid-19) had travelled back from northern Italy, where the virus was contracted.
Public Health Wales said medics were trying to trace people who had been in close contact with the patient.
Two further patients in England also tested positive for coronavirus, it was revealed on Friday.
Chief medical officer for England, Professor Chris Whitty said: “The virus was passed on in Iran and the patients have been transferred to specialist NHS infection centres at the Royal Free Hospital.
“The total number of cases in England is now 17. Following confirmed cases in Northern Ireland and Wales, the total number of UK cases is 19.”
People who sat within two rows of the coronavirus patient from Northern Ireland on the plane from northern Italy to Dublin have been contacted, health authorities said.
The latest cases came after Whitty had warned it was “just a matter of time” until coronavirus spreads further in the UK.
Schools could close for two months and sports fixtures cancelled, experts have warned.
Whitty said on Thursday that there could be a “social cost” if the virus intensifies, telling the Nuffield Trust summit: “One of the things that’s really clear with this virus, much more so than flu, is that anything we do we’re going to have to do for quite a long period of time, probably more than two months.”
So far in the UK, 7,690 people have been tested for the virus and of the 16 to have tested positive, eight have so far been discharged from hospital.
The Northern Ireland patient had recently returned from northern Italy, while a parent at a primary school in Derbyshire contracted the virus in Tenerife, where 168 Britons are being kept in a hotel on the south west of the island.
Burbage Primary School remains shut on Friday, with patients at Buxton Medical Practice – a two minute drive away – were told not to attend appointments on Thursday.
Speaking at a press conference in Belfast, Dr Michael McBride, chief medical officer for Northern Ireland, said the country had been planning for its first positive case, and it had been “a question of when not if”.
He added: “We have robust infection control measures in place which enable us to respond immediately.
“Our health service is used to managing infections and would assure the public that we are prepared.”
A special unit has been established at the Royal Victoria Hospital in Belfast for isolating those suffering from the virus but the health authorities were unable to confirm where the patient is being treated.
One of the patients in England has been taken to the specialist infectious diseases centre at the Royal Liverpool Hospital and the other to the Royal Free Hospital in London.
Meanwhile, 168 Britons remain confined to the H10 Costa Adeje Palace in Tenerife after four guests tested positive for the virus, but sources within the hotel told PA that around 50 people have been told they are allowed to leave if they wish to do so.
The Minister of Health in Tenerife said around 130 guests from 11 different countries will be able to leave the hotel if they arrived on Monday, after infected guests had already left.
But airline Jet2 has said it will not fly back any people who have been staying at the hotel until they have tested negative for the illness.
British Airways has confirmed it will cancel some flights to and from Italy, Singapore and South Korea, as a result of reduced demand for travel to the areas due to coronavirus outbreaks.
British Airways said on Thursday it would cancel 56 roundtrip flights from London’s Heathrow and Gatwick airports to Italian destinations including Milan, Bologna, Venice and Turin between March 14 and March 28.
Flights to Seoul, which are usually daily from Heathrow, will now be every other day, and BA said it was also cancelling six roundtrip flights from Heathrow to Singapore every other day from March 15, although there will still be one flight daily.
The airline said it would be contacting customers on cancelled flights to discuss their options, which would include rebooking onto other carriers if possible, full refunds or booking for a later travel date.
Two Britons were among eight people being monitored on board a cruise ship that was turned back by the Dominican Republic.
A joint statement by the Public Health Ministry and Port Authority on the island said the captain of the Braemar, which is carrying around 1,500 people, reported four Filipinos, two British citizens and two US citizens were under medical observation for symptoms such as fever, coughing, or breathing difficulty.
Speaking at a press conference on Thursday, World Health Organisation (WHO) director-general Dr Tedros Ghebreyesus said: “This virus has pandemic potential. This is not a time for fear.
“This is a time for taking action to prevent infection and save lives now.”
Financial markets have plunged as the number of new cases outside China continued to grow.
Share prices have plummeted, and are on track for the worst week since the global financial crisis in 2008 as the disruption brought by the virus fuelled fears of a recession both in the US and the Euro zone.
Countries other than China now account for around 75% of new infections. Four new countries have reported first cases – taking the total to 55 countries outside of China. Across these countries there have been around 3,700 cases reported, and an estimated 70 deaths.
The Swiss government has banned all events involving more than 1,000 people amid the coronavirus outbreak.
An Italian man who arrived in Nigeria this week was confirmed as the first coronavirus case in Africa’s most populous country, while a person who returned on a flight from Iran became the first in faraway New Zealand.
In Europe, France’s number of reported cases doubled, Germany warned of an impending epidemic and Greece, a gateway for refugees from the Middle East, announced tighter border controls. The death toll in Italy, Europe’s worst-hit country, rose to 17 and the number of people who tested positive for the illness increased by more than 200 to 655. Germany has about 45 cases, France about 38 and Spain 23, according to a Reuters count.Advertisement
South Korea has the most cases outside China, and reported 256 new infections on Friday, bringing its total infections to 2,022.
The head of the WHO’s emergency program, Dr Mike Ryan, said Iran’s outbreak may be worse than realised. The country has suffered the most deaths outside China - 26 from 245 reported cases.
As of Friday there were 200 confirmed cases in Japan, as all schools in the country were ordered to close and large gatherings scrapped. Four people have died, but the country has pledged that the Olympic Games will proceed as planned.
Four more deaths have been reported among passengers who had been on the quarantined Diamond Princess cruise ship. More than 700 people aboard tested positive for the virus.