The city of Wuhan has reported its first cluster of coronavirus infections since its lockdown was lifted a month ago.
The new cases in the epicentre of China’s COVID-19 outbreak will make stark reading for other nations, such as the UK, in the midst of easing their own lockdowns.
Wuhan reported five new confirmed cases, all from the same residential block.
One of those infected was the wife of an 89-year-old patient reported a day earlier in the city’s first confirmed case in more than a month.
The UK will be watching what happens in China closely as it begins to adapt its own restrictions.
From Wednesday, those who cannot work from home will be expected to return to the workplace while avoiding public transport, while people will be able to meet another person in a park if they keep two metres apart.
People in England should also aim to wear face masks on public transport and in some shops from Wednesday.
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A 50-page document on the new measures was published on Monday afternoon, while Johnson will also address Parliament and lead the government’s daily press briefing, which has been moved back to 7pm.
On Sunday, Johnson warned there could be a second wave of infections as the lockdown is eased.
“We have been through the initial peak – but it is coming down the mountain that is often more dangerous,” he said.
“We will be monitoring our progress locally, regionally, and nationally and if there are outbreaks, if there are problems, we will not hesitate to put on the brakes.
“It would be madness now to throw away that achievement by allowing a second spike. We must stay alert. We must continue to control the virus and save lives.”
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In Wuhan, all of the latest cases were previously classified as asymptomatic, meaning they tested positive for coronavirus and are capable of infecting others but do not show clinical signs such as fever.
"At present, the task of epidemic prevention and control in the city is still very heavy," the Wuhan health authority said. "We must resolutely contain the risk of a rebound."
The number of asymptomatic cases in China is not known, as they show up positive during tests conducted as part of contact tracing and health checks.
China does not include asymptomatic cases in its overall tally of confirmed cases.
According to Johns Hopkins University, there have been more than 84,000 cases in China and 4,637 deaths.
Hundreds of asymptomatic cases in Wuhan, which came out of its lockdown on 8 April, are being monitored.
The number of new cases reported in China since April have been small compared with the thousands confirmed every day in February, thanks to a nationwide regime of screening, testing and quarantine.