British Prime Minister Boris Johnson on Friday said he would continue his self-isolation after testing positive for COVID-19, following a week of staying at home and working remotely.

Johnson, 55, became the most high-profile world  leader to contract the virus when he announced he had tested positive last Friday.

He has been working from a flat above his Downing Street offices since then, and had been expected to re-emerge on Friday.

But he said in a video message on Twitter: "In my own case, although I'm feeling better and I have done my seven days of isolation, alas, I still have one of the minor symptoms... a temperature. So, in accordance with government advice, I must continue my self-isolation until that symptom itself goes."

Johnson, who in the video still looked under the weather and was seen wearing a shirt without a tie, on March 23 ordered a three-week countrywide lockdown to cut close-contact transmission of the virus.

That followed scenes in parks and the countryside of crowds of people flouting government guidance on social distancing, and concern about packed trains on the London Underground network.

In his latest message, Johnson warned people not to be tempted to venture outside at the weekend, with better, warmer weather forecast.

"I just urge you not to do that," he said. "Please, please stick with the guidance. This country has made a huge effort, a huge sacrifice, done absolutely brilliantly well in delaying the spread of the virus. Let's stick with it now."

Johnson, and his Health Secretary Matt Hancock, have been among nearly 34,000 people who have tested positive for COVID-19 in Britain.

Nearly 3,000 have died.