Around 80,000 people in England will be offered urgent tests for the South Africa coronavirus variant after cases with no links to travel were found.

Residents aged 16 and over in eight areas across Surrey, London, Kent, Hertfordshire, Southport and Walsall are being asked to take tests, regardless of symptoms.

The health secretary said the UK must come down "hard" on the variant .

Previous cases in the UK were connected to South Africa.

But random checks found 11 cases that could not be linked to international travel.

Matt Hancock told a Downing Street news conference on Monday that there was "currently no evidence" to suggest the South African variant was "any more severe, but we need to come down on it hard, and we will".

The neighbourhoods being targeted for testing are:

• W7, N17 and CR4 in London

• WS2 in Walsall

• ME15 in Maidstone, Kent

• PR9 in Southport

• EN10 in Broxbourne, Hertfordshire

• GU21 in Woking

Appealing to residents of these postcodes, Mr Hancock added: "It is imperative that you stay at home, and that you get a test, even if you don't have symptoms.

"This is so important so that we can break the chains of the transmission of this new variant, and we've got to bring this virus to heel."

Prof Adam Finn, a member of the Joint Committee on Vaccination and Immunisation (JCVI), said a "real effort" should be made to try to "eliminate" the South African variant before it took hold.

Prof Jim McManus, the director of public health for Hertfordshire, said if every single case was detected, it might be "possible" to eradicate the variant within two weeks.

He warned that officials "may find this has spread beyond that, so it may take three weeks or more, but we will give this everything we have got," he told the BBC.

Asked about the effectiveness of vaccines against the South African strain, Dr Susan Hopkins, strategic response director at Public Health England, said: "Three of the vaccines that have been used to date in the trials have shown that they've been effective against the South African variant at a level greater than was set as the minimum standard by the WHO.

"We expect all other vaccines to have a similar level of effectiveness, particularly in reducing hospitalisation and death."

Almost 9.3 million people in the UK have now received a first dose of a coronavirus vaccine, according to the latest government figures.

Meanwhile, a further 18,607 new infections were recorded in the UK as of Monday, as well as another 406 deaths within 28 days of a positive test.

In total, 105 cases of the South African variant have been identified.

The 11 cases are not tied to people who had travelled to South Africa, or to the other known cases, prompting fears they may have caught it in the UK.

And the government has now advised local authorities to begin mass testing in a number of neighbourhoods where these cases have been identified.

In some areas, home testing kits are also being sent to households.

Positive cases will be analysed to see if they are caused by the South African variant.