Britain's Johnson warns that health service could be overwhelmed by coronavirus

Britain has urged 1.5 million people identified by the NHS as being at higher risk of severe illness if they contract coronavirus to not leave their homes, to protect themselves.

Johnson also advised people to keep away from elderly parents on Sunday, which is Mothering Sunday in Britain.

But physical distancing and strict restrictions on social activity are not enough to defeat COVID-19, the disease caused by the coronavirus, the World Health Organization's (WHO) top emergency expert Mike Ryan said.

"What we really need to focus on is finding those who are sick, those who have the virus, and isolate them, find their contacts and isolate them," Mike Ryan said in an interview on the BBC's Andrew Marr Show.

"The danger right now with the lockdowns ... if we don't put in place the strong public health measures now, when those movement restrictions and lockdowns are lifted, the danger is the disease will jump back up."