PHE defines such areas as those “where there is divergence from the measures in place in the rest of England because of the significance of the spread, with a detailed action plan in place, and local resources augmented with a national support”.
Luton, in Bedfordshire, has also been upgraded to an “area of intervention”, though its rate of cases has gone down.
“We are very grateful to our communities for working with us,” Mr Khan said.
The leader of Blackburn with Darwen Council has told local residents it is “sensible not to relax” lockdown restrictions, as the rate of Covid-19 cases in the borough has shot up.
Councillor Mohammed Khan urged the community to “keep up the momentum” in combating the disease as 122 new coronavirus cases were recorded in the seven days to 20 July.
Public Health England (PHE) has upgraded Blackburn with Darwen to an “area of intervention” following the increase, which was the highest at local level.
“The increase in testing is helping to ensure that we are heading in the right direction with a reduction in positive cases and hospital admissions.
“We need to keep up the momentum with our strong prevention work so we agree it’s sensible not to relax the easing of restrictions at the moment to stop the spread.”
Mr Khan added that the decision to delay the reopening of council leisure facilities would run alongside new “localised prevention measures”.
“We feel that accelerating our control measures in this way will assist us to move out of having higher Covid rates even faster – we are grateful for the government’s help in our local plans on this,” he said.
The rate of cases in Blackburn with Darwen has jumped from 49.7 cases per 100,000 in the seven days to 13 July to 81.9 in the seven days to 20 July.
In Luton, the rate fell to 24.8 cases per 100,000 in the week to 20 July from 31.8 the previous week.
Nevertheless, Luton Borough Council said it had agreed with government officials that gyms, pools, and other leisure facilities would not reopen as planned on 25 July.
Hazel Simmons, the council leader, said: “Our main priority is to protect Luton and these measures only serve to underline the importance of doing just that. Please pass these important messages on to your family and friends and if you can, stay at home.
“Fighting coronavirus is everyone’s responsibility. Too many families and friends have lost loved ones and we must do everything we can to ensure more lives aren’t wasted unnecessarily.
“There has been too much heartache in the town for us to risk further anguish, pain and suffering.”
It came as NHS Test and Trace chief Baroness Dido Harding said that there were still concerns surrounding northern towns including Blackburn, Bradford and Leicester.
She told the BBC that there were “a number of areas in the North West that we are working really closely with”.
Lady Harding added there were particular concerns about coronavirus spreading in South Asian communities in England.
“We are all learning what makes different communities, different professions, different parts of the country more vulnerable,” she told the broadcaster.
“I don’t think there’s a simple answer to say why one place and not another.
“There are a mix of things – certainly we are seeing a very high prevalence in the South Asian community across the country.”