Scientific advisers in Wales believe the UK is at the “pre-peak stage of a third wave”, first minister Mark Drakeford has warned.
Mr Drakeford told a press conference eight out of 10 new cases of coronavirus in Wales are believed to be from the Delta variant.
“In just a few weeks, the Delta variant has entered Wales and spread quickly throughout the country,” he said.
“There is a sustained and accelerating pattern of transmission, not just in the north and southeast of Wales but in all parts of the country.
“That means that we are, once again, facing a serious public health situation. Our scientific advisers believe the United Kingdom is now at the pre-peak stage of a third wave of this pandemic.
“Wales may be two to three weeks behind what is happening in England and in Scotland, where tens of thousands of cases have been confirmed, where there is widespread transmission and reports of increased hospital admissions as well.”
Mr Drakeford said both Nicola Sturgeon and Boris Johnson had paused plans to relax coronavirus restrictions due to the Delta variant.
"Today, I have to announce that we will be doing the same in Wales," he added.
The Welsh government will pause further easing of coronavirus restrictions for four weeks to allow for more people to be vaccinated, Mr Drakeford told reporters.
He said this would help Wales, which has the lowest Covid-19 rates in the UK, “manage the impact of this new wave of infections”.
“A four-week delay could help to reduce the peak number of daily hospital admissions by up to half,” Mr Drakeford said.
Delta variant infections in the UK have jumped by 78 per cent in just one week, according to the latest Public Health England (PHE) data.
The number of confirmed Covid-19 cases involving this more transmissible variant - also known as the Indian variant - rose by 33,630 to 75,953 over seven days, with general coronavirus infections now at their highest levels in the UK since mid-February.
Additional reporting by PA