LONDON (REUTERS) - Countries can't simply lock down their societies to defeat coronavirus, the World Health Organisation's top emergency expert said on Sunday (March 22), adding that public health measures are needed to avoid a resurgence of the virus later on.

"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," Dr 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."

Much of Europe and the United States have followed China and other Asian countries and introduced drastic restrictions to fight the new coronavirus, with most workers told to work from home and schools, bars, pubs and restaurants being closed.

Dr Ryan said that the examples of China, Singapore and South Korea, which coupled restrictions with rigorous measures to test every possible suspect, provided a model for Europe, which the WHO has said has replaced Asia as the epicentre of the pandemic.

"Once we've suppressed the transmission, we have to go after the virus. We have to take the fight to the virus," Dr Ryan said.

Italy is now the country worst hit by the virus in terms of the number of deaths, and British Prime Minister Boris Johnson has warned that his nation's health system could be overwhelmed unless people avoid social interactions. British housing minister Robert Jenrick said that production of tests would double next week and ramp up thereafter.

Dr Ryan also said that several vaccines were in development, but only one had begun trials in the US. Asked how long it would take before there was a vaccine available in Britain, he said that people needed to be realistic.

"We have to make sure that it's absolutely safe... we are talking at least a year," he said.

"The vaccines will come, but we need to get out and do what we need to do now."