U.K. Prime Minister Boris Johnson on Thursday gave a stark assessment of the coronavirus pandemic, calling it the “worst public health crisis for a generation” and telling British families that many are going to lose loved ones because of the virus.

“This is the worst public crisis for a generation, some people compare it to seasonal flu, alas that is not right," he said. "Owing to the lack of immunity, this disease is more dangerous and it’s going to spread further."

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"I must level with the British public, many more families are going to lose loved ones before their time,” he added.

Johnson addressed reporters after holding an emergency COBRA meeting of top Cabinet officials to discuss the growing global pandemic.

The prime minister held off from certain measures that other European countries had taken, such as banning large public gatherings and shutting down schools, but said that the government was advising anyone with a fever or persistent cough to stay at home for a week. He said the government may soon recommend that entire households self-isolate, but that it was not issuing that advice at this time.

On closing schools, he said that the scientific advice was “this could do more harm than good at this time.” His remarks come hours after Irish Prime Minister Leo Varadkar announced that all schools, universities and other public facilities will be closed and teaching will be done online or remotely.

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“We have not witnessed a pandemic of this nature in living memory and this is uncharted territory for us,” Varadkar said from Washington, D.C.

While Britain has so far been spared the kind of significant spread that other countries such as Italy have suffered, the country has 590 confirmed cases and at least 10 deaths. But Patrick Vallance, the government’s chief scientific adviser, said the number of infected could rise to 10,000.

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Vallance also said that the government believes that the peak might be 10 to 14 weeks away. About 95 percent who will be infected could be struck over a nine to 10-week period on either side of that peak.

The officials showed a graph showing the predicted peak, with a sharp increase and decline on either side of it. Johnson made reference to that graph when he urged Brits with symptoms to self-isolate, saying it would “help us delay and flatten the peak, squash that sombrero.”

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Britain was given a boost on Wednesday night when President Trump announced a European travel ban but excluded both the U.K. and Ireland from the restrictions.

“The U.K. basically has got the border, strong borders and they're doing a very good, job, they don't have much infections and hopefully they'll keep it that way,” he said. Johnson is a close ally of Trump, who has in turn supported Johnson's push to take Britain out of the European Union.

Fox News' Chris Irvine and The Associated Press contributed to this report.