The county borough of Caerphilly in south Wales is to be placed under a local lockdown following a "significant rise" in coronavirus cases.
People will not be allowed to enter or leave the area without a reasonable excuse when the restrictions come into force from 6pm on Tuesday, the Welsh Government said.
Everyone aged over 11 will be required to wear face coverings in shops – marking the first time this will be mandatory in Wales.
Meetings with other people indoors and extended households will not be allowed, while overnight stays will also be banned.
There have been 133 new Covid-19 cases in Caerphilly county borough over the past seven days, equivalent to a rate of 55.4 cases per 100,000 population.
The latest number of confirmed cases of Coronavirus in Wales has been updated.
— Public Health Wales (@PublicHealthW) September 7, 2020
This is the highest rate in Wales and one of the highest in the UK – and case numbers are expected to rise, the Welsh Government said.
Health minister Vaughan Gething said: "We have seen a significant rise in cases in Caerphilly borough over a very short space of time, which are linked to holiday travel abroad and people socialising indoors and not following social distancing guidelines.
"A lot of these cases are in younger people and thankfully, at the moment, most of these are mild.
Coronavirus laws will be tightened across Caerphilly borough to prevent a local outbreak of the virus spreading, Health Minister Vaughan Gething said tonight. PLEASE SHARE to help #KeepCaerphillySafehttps://t.co/BFSAzk6Cja@PublicHealthW@AneurinBevanUHB@WelshGovernmentpic.twitter.com/wlbDumkUD5
— caerphillycbc (@CaerphillyCBC) September 7, 2020
"But coronavirus is now circulating in the community and it's only a matter of time before we start to see more serious cases, which need hospital treatment.
"We need the help of everyone in Caerphilly borough to prevent the increasing and onward spread of coronavirus.
"We can only bring this local outbreak under control if everyone pulls together and follows these new steps.
"If we do not see cases falling, we may need to take further steps to bring this local outbreak under control."
Community testing was introduced in Caerphilly at the weekend.
On Saturday, 450 people were tested and 19 had the virus – giving a positivity rate of 4%, which indicates that Covid-19 is circulating in the community.
Here's an appeal from the Leader of Council, Cllr Philippa Marsden, asking everyone to do their bit to control the spread of coronavirus. PLEASE SHARE to help #KeepCaerphillySafe@PublicHealthW@AneurinBevanUHB@ChristinaHarrhypic.twitter.com/sBZ14dn2d2
— caerphillycbc (@CaerphillyCBC) September 5, 2020
A similar number of people were tested on Sunday, with results expected shortly.
Travel restrictions included in the lockdown mean people cannot enter or leave Caerphilly County Borough Council area without a "reasonable excuse".
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.
People will only be allowed to meet others outdoors, with indoor meetings and gatherings restricted.
Caerphilly Council has already introduced measures such as suspending care home visits, and introducing weekly testing for care home staff, in response to the increase in cases.
Philippa Marsden, leader of Caerphilly Council, said: "We need to create a break in the cycle of infection we are seeing in Caerphilly borough at the moment and unfortunately that means introducing new, tougher restrictions.
"I would urge everyone living in the area to follow these new measures; to follow the social distancing guidelines and to wash their hands regularly.
"If we all work together, we can bring this outbreak under control and reduce cases of the virus."
The new measures will be enforced by the local authority and police.
Earlier on Monday, Public Health Wales reported the highest number of positive Covid-19 cases in months and warned of a "significant" rise in the Caerphilly area.
It said that a further 133 people had tested positive for coronavirus, representing the highest daily figure since June 27, when 140 cases were reported.
There were no further deaths in people with coronavirus, with the total in Wales since the beginning of the pandemic remaining at 1,597.
Numerous schools have been affected by coronavirus since the start of the autumn term, including one class of 21 pupils at a primary school in the Caerphilly area being told to self-isolate for 14 days.
Dr Giri Shankar, of Public Health Wales, appealed to everyone in the Caerphilly area to use a local testing unit at the town's leisure centre if they were experiencing "even the mildest" of symptoms or feeling "generally unwell with no explanation".