Health officials have raised concerns over the “significant rise” in coronavirus cases in the Merthyr Tydfil and Rhondda Cynon Taf areas of south Wales.
Public Health Wales said the increase in transmission appeared to be due to a lack of social distancing by people of all ages in a range of locations.
Today, the number of positive cases in Wales increased by 165 – representing the highest daily figure since May 20, when 166 were reported.
A local lockdown began in Caerphilly county borough yesterday evening, while travellers arriving in Wales from the Greek islands of Santorini, Serifos and Tinos now have to self-isolate for 14 days.
Dr Giri Shankar, from Public Health Wales, said: “We are concerned at the significant rise in positive coronavirus cases in the Merthyr Tydfil and Rhondda Cynon Taf areas over the past few days, and our investigations indicate that a lack of social distancing by people of all age groups in a range of different locations has resulted in the spread of the virus to other parts of the population.
“It appears that as lockdown restrictions have eased, people have taken advantage of the greater possibilities for activities, but they seem to have forgotten the importance of social distancing – resulting in possible transmission in the wider community.
“It is clear that the virus spreads more easily in indoor settings, and people should take extra care to socially distance in these cases to keep themselves and their friends and families as safe as possible.”
Dr Shankar said Public Health Wales supported the local lockdown restrictions in Caerphilly, which he said were “essential” to limit the spread of Covid-19.
Under the measures, everyone aged over 11 must wear a face covering in indoor spaces such as shops.
Travel in and out of the county is limited to those with a “reasonable excuse”, and people from different households are not allowed to meet indoors.
Local authority leaders, the health board and Dyfed-Powys Police cautioned people in the Carmarthenshire, Pembrokeshire and Ceredigion region that a local lockdown could happen if they did not socially distance.
The warning came after a cluster of coronavirus cases were confirmed in Carmarthenshire, centred around a community event.
Figures released by Public Health Wales on Wednesday showed there have been no further deaths in people with coronavirus, with the total in Wales since the beginning of the pandemic remaining at 1,597.