Lockdown restrictions are set to come into force in Cardiff and Swansea county areas and also the town of Llanelli.
They will come into effect in Llanelli, Carmarthenshire on Saturday at 18:00 BST and in Wales’ two biggest cities on Sunday from 18:00.
It will mean eight counties will be under lockdown and one town in a ninth.
On Thursday, there were 25 new cases in Carmarthenshire, 39 in Cardiff and 41 in Swansea.
People in Cardiff and Swansea should not “treat this weekend as a final blow-out”, Wales’ Health Minister Vaughan Gething said.
He also said cases in Carmarthenshire had “overwhelmingly” been linked to Llanelli, with eight out of 10 cases there.
The Llanelli lockdown is the first not to cover a whole local authority area. A postcode finder will be made available online to make clear which areas are under lockdown, said Mr Gething.
The majority of cases in Llanelli have been linked to people socialising without social distancing.
Burry Port will not be included in the area under restrictions.
People living in Caerphilly, Rhondda Cynon Taf, Bridgend, Blaenau Gwent, Merthyr Tydfil and Newport already cannot leave their areas without a reasonable excuse, under rules in place.
The changes mean around 1.5 million people will be under local lockdown, a little under half the Welsh population.