Welsh leaders on Friday announced Cardiff will become the first UK capital city to go into local lockdown since a national shutdown earlier this year, as London's coronavirus rates also rose.

The restrictions, which bar people from entering or leaving areas unless for work, education or another valid reason, will also apply in second city Swansea, from 6pm (1700 GMT) Sunday, and in the town of Llanelli from Saturday.

The new rules, which also forbid people meeting anyone not in their household indoors, follow a nationwide surge in coronavirus cases that has intensified across south Wales.

The devolved government, which is responsible for healthcare, said ministers will hold discussions over the weekend with health experts and others to consider if the measures need to be imposed elsewhere.

"We're acting to protect people's health and to try and break the chain of transmission and stop the situation from getting worse," Welsh Health Minister Vaughan Gething said.

The announcement of the new shutdowns came as the UK government said the so-called R number -- the virus' reproduction rate -- across Britain was now between 1.2 and 1.5 and growing.

That means on average every 10 people infected will infect between 12 and 15 other people, with scientists estimating new cases were growing four to eight percent every day.

In London, the growth rate is four to nine percent, and Mayor Sadiq Khan warned the capital was at a "very worrying tipping point".

He said there had been a sharp rise in hospital admissions and patients in intensive care, and called for more testing in the city, accusing ministers of diverting capacity elsewhere.

"The lack of testing capacity is totally unacceptable and it is why London has been added to the government's coronavirus watchlist as an area of concern," he said.

"Ministers simply have to get a grip.... Any delay will mean letting the city down and will cost lives."

UK Prime Minister Boris Johnson on Tuesday announced a raft of new restrictions in England, mirrored to varying extents in the UK's other nations, to try to curb the rise.

They include a 10:00 pm curfew for pubs, bars and restaurants, which came into force on Thursday night, and again encouraging people to work from home if they can.

Large swathes of northern and central England were already under tighter restrictions than the rest of the country following spikes in Covid-19 cases there.

Local leaders in Leeds said on Friday it was likely the northern English city would face new rules from midnight, including a ban on households mixing in private homes.

That would take the number of people living under local restrictions to more than 16.2 million people across the UK, according to an assessment by the domestic Press Association news agency.

Britain has been the worst-hit country in Europe by the pandemic, with the government recording nearly 42,000 deaths of people who had tested positive for Covid-19.