Four new cases of coronavirus were confirmed in the UK on Sunday as experts warned of an impending pandemic, with parts of Italy in lockdown after a huge rise in the number of new infections.

The new British patients had all been passengers on the Diamond Princess cruise ship and were in quarantine on the Wirral when they fell ill, having returned from Japan on Saturday.

It emerged on Sunday that the patients had been tested while in Japan but the results were not received until Sunday morning, by which point they were back in the UK. They have now been transferred to specialist NHS infection centres.

Of the four people who tested positive, two are in the Royal Hallamshire Hospital in Sheffield, one is in the Royal Liverpool University Hospital and the fourth was taken to the Royal Victoria Infirmary in Newcastle, NHS England said.

Professor Keith Willett, the NHS strategic incident director for coronavirus, said: "These specialist centres are well prepared to deal with cases and, earlier this year, the Newcastle unit successfully treated and discharged two patients who had contracted the virus."

It brings the total number of UK cases to 13 and comes as the European threat from coronavirus dramatically increased, with four deaths in northern Italy having followed the diagnosis of more than 152 cases.