Prime Minister Boris Johnson is warning Britons in a letter to 30 million households that things will get worse before they get better, as he himself self-isolates in Downing Street to recover from the coronavirus.

Britain has reported 17,089 confirmed cases of the disease and 1,019 deaths and the peak of the epidemic in the country is expected to come in a few weeks.

In the letter to be delivered to homes, Johnson urges people to stick with the lockdown measures that his government has imposed to try to prevent the state National Health Service from being overwhelmed by a surge of cases.

“We know things will get worse before they get better,” Johnson writes. “At this moment of national emergency, I urge you, please, to stay at home, protect the NHS and save lives.”

Senior minister Michael Gove said on Sunday the government is “very concerned” about the death toll.

He also said the country has boosted the amount of testing for the virus.

“The number of tests being carried out has hit 10,000 a day. We want to increase that to 25,000 a day.”