Blackburn is facing a “rising tide” of coronavirus cases, centred on its large Asian community, with two weeks to get the numbers down before lockdown measures are reversed, the area’s public health director warned.

The Lancashire town brought in extra restrictions on Tuesday and Professor Dominic Harrison, the local authority’s director of public health, said the borough of 148,000 people was facing a “rising tide” of cases.

Prof Harrison, speaking on BBC Radio 4’s Today programme, said: “We have what we call a rising tide event rather than an outbreak, and by that we mean that we’ve got a number of cases rising in specific areas across a significant community, but not a single big outbreak like Kirklees or other areas that had a workplace outbreak.

“It can have the same effect because it can drive up the cases, but what we are seeing from looking at the postcode data of those cases is, in the last couple of weeks, is that what we are seeing is a single case being infected, then going back to a household and all that household becoming infected.

“And when we look at the data what we can see is clusters in a part of the town, but the clusters are household clusters, so a number of those are causing the rising tide event and we know that they are in mainly south-Asian areas, and they are in areas with high number of terraced houses with high numbers of occupants in the house, so four or more, five or more people in the household.”

He said the Blackburn with Darwen borough, which has an Asian population of about 28%, had 114 cases in the last two weeks and 97 of those cases are south Asian.

The rate of confirmed cases per 100,000 has gone up to 47 per 100,000, up from 31.6 cases in the seven days to July 4.

The authority is third on the list of highest weekly rates, behind Leicester, which has a rate of 118.2 cases per 100,000 and is subject to a local lockdown, and nearby Pendle, with a rate of 76.6.

Prof Harrison said this has triggered the local response, with the establishment of an outbreak control management board and five extra measures introduced.

These are to reduce household visiting to one household plus two members from another household, face masks in all pubic spaces, inspections on small corner shops, asking people not to hug or shake hands on greeting, and increased testing with mobile testing units and targeted testing units.

Prof Harrison added: “If numbers are not turning round and going down again by July 27, so two weeks, we are going to then have our next stage, we will go through the lockdown lifting measures and reverse them one by one until the numbers go down.

“But we’re not going to go from no lockdown and everything open to everything shut, as Leicester has.”

Council leader Mohammed Khan said: “I can reassure all local residents that the council is working with different agencies and organisations across the borough to help get the message out to everyone that life cannot go back to normal just yet, and we must all make sacrifices to avoid a local lockdown.

“Please continue to do your bit to stick to the rules to protect yourself and your family.”

In Pendle, people were also warned to stay alert after the authority reported an increase in cases, particularly in Nelson and Brierfield.