An extra 11,000 positive coronavirus tests missing from official figures in Wales demonstrate "how serious the position" in the country is, First Minister Mark Drakeford has said.
Maintenance work on Public Health Wales systems at the end of last week meant the numbers were not included on top of 11,911 positive cases reported by the agency between 9 and 15 December.
Today, Mr Drakeford denied the data had been "missing" from the country's figures in recent days and was known by the Welsh Government.
He told BBC Breakfast: "This was planned upgrading of the computer system, none of the data is missing, everybody who had a positive test in Wales was told that last week, everything was uploaded on to our Track, Trace and Protect system.
"But the figures do demonstrate just how serious the position here in Wales has become and underlines why we made the decisions yesterday both in the lead-up to Christmas, during Christmas, and once Christmas is over.
"The Government was aware that there were tests that are being carried out which were not being loaded on to the system because that is what we already announced."
A statement from Public Health Wales said its dashboard was being updated with the figures following the work on its NHS Welsh Laboratory Information Management System (WLIMS).
It said: "This means that we expect a backlog of results to come through over the coming days, and there will be a period of data reconciliation and validation that will affect our daily reporting figures for several days.
"(Thursday's) figures and those over the following days will be higher as a result of the backlog coming through."
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Meanwhile, UK Health Secretary Matt Hancock is expected to only make minor changes to the tiering allocations for coronavirus restrictions ahead of the Christmas easing of measures.
Mr Hancock will update MPs today.
Greater Manchester mayor Andy Burnham said there is a "clear case" for his region to go down to Tier 2.
But he said he fears ministers will "overcompensate" because of the decision to allow the Christmas easing of restrictions to go ahead despite warnings it will lead to a spike in infections and deaths.
The PA news agency has been told Mr Hancock will not make many changes to the current tier allocations.