People in Diss and Roydon are being “strongly encouraged” to take a coronavirus test to suppress the spread of a Covid-19 variant.
Surge testing is being deployed within parts of the IP22 postcode where the Covid-19 variant first identified in South Africa has been found.
Tests of all adults in Diss and Roydon will begin on Friday.
Dr Louise Smith, Norfolk County Council's director of public health said, in a tweet last night: "This is a precaution to find South African variant virus. Overall numbers in area are going down. No need for people to worry."
But people in Diss and Roydon are strongly encouraged to take a coronavirus test this week, whether they are showing symptoms or not.
People with symptoms should book a test in the usual way.
The Department of Health and Social Care said it was working in partnership with the local authorities.
It aims to help scientists and public health officials learn more about the mutated Covid-19 variant.
It will also help reduce the spread of infection by finding asymptomatic cases and prompting people to self-isolate.
In a statement, officials said surge testing was being introduced “in addition to existing extensive testing, and in combination with following the current lockdown rules”.
“Positive cases will be sequenced for genomic data to help understand Covid-19 variants and their spread within these areas,” it added.
Dr Smith said: “We’ve been working with the DHSC and PHE on tracing cases of this variant, and have agreed a programme of local testing in the Diss and Roydon areas.
"We will be sharing more details with residents over the next few days.”
Dr Smith had said there were between five to 10 cases of Covid-19 which had been identified as being the South African variant.
She had said all those cases were linked to people who had travelled to or from South Africa.
As well as Norfolk similar surge testing is also being deployed in parts of Southampton and Woking in Surrey.
Efforts in Manchester to track down examples of the mutation of the more transmissible Kent variant will also be expanded following deployment of testing teams last week, with the postcode districts of M40 and M9 set to be targeted.
Some 10,000 extra tests were rolled out in areas of the city last week after four people from two unconnected households were found to be infected with the E484K mutation, which is linked to the Kent variant mutation.
Laboratory studies have shown that viruses with the E484K mutation, which is also found in the South African variant, can escape human defences, making them more efficient at evading natural and vaccine-triggered immunity.
DHSC said surge testing in parts of the London boroughs of Haringey and Merton, along with Sefton in Merseyside, were complete.
"Further data on surge testing will be provided in due course," a spokeswoman said.
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