A new strain of coronavirus which could be behind the steep rise in cases in the south of England is already present in Wales.
There are at least 10 confirmed cases in the country and more are expected to be identified.
The Welsh Government said: “It is natural for a virus to mutate over time and we have seen a range of mutations in Wales.
“In relation to this particular mutation, we have identified 10 confirmed cases and five probable cases through sequencing that took place during November. Further sequencing is under way and we expect to identify further cases.
“Public Health Wales is actively looking for this variant and will be tracking any other Welsh cases as they emerge. Our findings will be feeding into the work being undertaken across the UK.”
The main concern about the new variant is that it appears to spread more quickly than the existing virus, with more than 1,000 cases found so far in 60 local authorities, predominantly in the South of England.
Matt Hancock, the Health Secretary, said there was “nothing to suggest” it caused worse disease or that vaccines would no longer work.