Surge testing has been deployed to a town after a cluster of the India Covid variant was found.
Areas within the BL3 postcode in Bolton registered a small number of cases of the variant, leading to widespread testing.
NHS Test and Trace said some cases of the coronavirus variant first identified in South Africa have also been found.
People who tested positive for the disease have been asked to self-isolate and their contacts have been identified, Public Health England said.
All residents have been asked to take a Covid-19 PCR test even if they have no symptoms.
Meanwhile, people with symptoms should book a free test online or by phone so they can get tested at a testing site or have a testing kit sent to them at home.
Those without symptoms should visit the local authority website for more information.
The Indian variant has been identified as a variant of concern by Public Health England and has caused a rise in transmission in parts of Bolton.
Weekly data shows that Bolton in Greater Manchester had the second highest Covid-19 case rate in England for the seven days to May 2, up from 48.0 to 85.2.
Dr Susan Hopkins, Covid-19 strategic response director at PHE, said: "The way to limit the spread of all variants is the same and although we are all enjoying slightly more freedom, the virus is still with us.
"Keep your distance, wash your hands regularly and thoroughly, cover your nose and mouth when inside and keep buildings well ventilated and meet people from other households outside.
"If you are told to get a test, if you have any symptoms at all or have been in contact with someone who has tested positive, please make sure you get tested too."
The Prime Minister said that tracking of the Indian variant was "absolutely ruthless".
Boris Johnson told reporters: "What we're doing there is making sure that we are absolutely ruthless in the surge testing, in the door-to-door tracking of any contacts.
"At the moment we're looking carefully at the way the Indian variant seems to function, we don't see any evidence that it is resistant to the vaccines or in any way more dangerous."
Current evidence suggests that the two other variants detected in India are not variants of concern.
