Under the restrictions, people will not be able to enter or leave the Rhondda Cynon Taf council area without a reasonable excuse.
The measures will apply in Rhondda Cynon Taf, south Wales, from 6pm on Thursday, the Welsh Government has announced.
Rhondda Cynon Taf, in south Wales, has seen a rolling seven-day case rate of 82.1 per 100,000 people. The Welsh Government has since introduced new measures to curb the virus’ spread
Households will no longer be able to meet each other indoors or form extended groups.
A British county will be placed under local lockdown after a rise in coronavirus cases.
This includes work, if people are unable to work from home, as well as making a compassionate visit to a loved one or to provide care.
Schools are still expected to remain open long with premises such as pubs and shops, Wales Online reports.
All licensed premises will have to close at 11pm.
The county borough, which has a population of around 240,000, has witnessed a rolling seven-day case rate of 82.1 per 100,000 people.
It is not yet known how long the lockdown will remain in place.
The new measures will be enforced by the local authority and the police.
“We now have evidence of wider community transmission in the borough, which means we need to take urgent action to control and, ultimately, reduce the spread of the virus and protect people’s health.
Health Minister Vaughan Gething said: “We have seen a rapid rise in cases in Rhondda Cynon Taf in a very short space of time, linked to people socialising indoors and not following social distancing guidelines.
“We need the help of everyone across Wales to prevent the increasing and onward spread of coronavirus. We can bring coronavirus under control if everyone pulls together and follows the rules we have put in place. They are there to protect you, your family, and your community.
The government added in a statement: “Contact tracing teams have been able to trace about half of the cases back to a series of clusters in the borough.
“Coronavirus has not gone away. It is still circulating in communities across Wales. Its vital people stick to the rules.”
“The rest are linked to community transmission.