The Welsh Health Minister Vaughan Gething has said on Tuesday that Caerphilly will be in lockdown until at least October.
The Welsh town which has around 181,000 resident will be placed into a local lockdown from 6pm on Tuesday evening.
This comes after 187 people tested positive for coronavirus over the last two weeks, data from Public Health Wales shows.
This puts the rate at 103.3 per 100,000 per population, while the rest of Wales is at 26.3.
Over the past two weeks more than 4,000 tests have been carried out in Caerphilly, with 4.4% proving positive, compared to 1.7% across Wales.
Family and friends who live separately will not be allowed to meet indoors or stay overnight, and no one will be allowed to leave the county, unless they have a good reason to do so.
Gething blamed the breakdown in “social distancing” in “large parts,” which forced the local lockdown.
Speaking to the Today programme the Welsh Health Mnister said, “If we had testing positivity rates of 4% [across Wales], I think we would be into national lockdown.”
He told BBC Radio Wales, “Even a week ago we comfortably had the lowest rate of coronavirus of any of the UK nations. We’re now in a position a week later where we’ve seen a significant spike in activity.
“If we don’t address the issue in Caerphilly, we’ll see wider community transmission within the Caerphilly area but that will spread to other areas as well.
“We’re in this position largely because social distancing has broken down and in particular people are socialising in each other’s households in larger numbers.
“The reasons for the local lockdown are a spike in transmission that if left unaddressed will go out of control and will see more people get it, will see more people in hospital, will see more people seriously unwell and will then have national consequences.”
He appealed for people to “please follow the rules. It’s for you, your family and the whole community.”
Gething said transmission is not taking place in pubs, it is an element of people returing from European holidays then socialising with others at home.
The exemptions for people being allowed to leave Caerphilly are “if you have to go to work, if you have caring responsibilities or if you absolutely have to move house, that should be covered but going from Caerphilly to Cardiff for a night out or to go to the gym isn’t covered.
“If things deteriorate faster, we may have to take more measures.”
“We’re in it for several weeks at least in Caerphilly. We expect the rate to rise in the next few days because community transmission has already taken place.
“I can’t over-state the seriousness of the situation that we are in.”