The British government on Thursday extended lockdowns to Liverpool and several other towns in northern England, effectively putting more than a quarter of the country under tighter coronavirus restrictions.

Health Secretary Matt Hancock said limits on social gatherings would be extended to the Liverpool City region, which has a population of about 1.5 million.

Similar measures to limit socialising and trips outside the home were imposed in nearby Warrington, also in the northwest, and Middlesbrough and Hartlepool in the northeast.

Before the announcement, some 16 million people of the UK's 66.8 million people were already under some local restrictions, according to the main opposition Labour party.

London is currently exempt but the capital is on alert due to rising cases and hospital admissions.

The new rules in Liverpool will ban mixing between different households except outdoors, and residents were advised to avoid care homes and only travel for "essential" reasons, which include school or work.

Prime Minister Boris Johnson said Wednesday he was keen to avoid a nationwide stay-at-home order of the kind imposed in March, when coronavirus first swept across Britain.

But he said he was prepared to take further action if the upward trend continued.

More than 42,000 people have died from the virus so far in Britain, the highest toll in Europe.

The UK-wide lockdown was eased in June but a recent rise in cases has alarmed authorities.

In addition to the localised restrictions placed on towns and cities, devolved governments in England, Wales, Northern Ireland and Scotland have imposed rules across their nations restricting social contact, particularly in private homes.

In a rare piece of good news, researchers involved in a mass testing programme at Imperial College London said Thursday they had seen signs that the growth of infection was slowing.

The survey, which involved 80,000 volunteers tested in England between September 18 and 26, found around 1 in 200 people were infected.

Professor Paul Elliott, director of the programme, said: "The growth of new cases may have slowed, suggesting efforts to control the infection are working."

However, he added: "The prevalence of infection is the highest that we have recorded to date. This reinforces the need for protective measures to limit the spread of the disease."