Hospitals in the Cwm Taf Morgannwg University Health Board have suspended all "non-urgent" surgeries and appointments after an "alarming" increase in coronavirus cases in Bridgend, Rhondda Cynon Taf and Merthyr Tydfil.
They are standing down services so staff can to be redeployed to core and emergency services across the area.
It is the third health board to take this step. Swansea Bay University Health Board has postponed some non-urgent surgery at Neath Port Talbot Hospital and all non-essential face-to-face appointments at all its sites, while Aneurin Bevan University Health Board has postponed all non-urgent care.
Urgent cancer services and clinically urgent patients will continue to be seen.
In a statement the health board said: “Such is the pressure in our areas of Bridgend, Rhondda Cynon Taf, and Merthyr Tydfil that in the last week the equivalent of almost 4 people acquired the virus every 10 minutes.
"The transmission rates in our council areas are in the highest 20 areas in the whole of the UK.
"This decision has not been taken lightly as we know it will mean people in our communities will not be able to access some local NHS services and many patients will have to wait longer for outpatient appointments and operations.
"However the rates of transmission and the associated rise in hospital admissions mean that there is no choice if we are to keep essential and emergency services running."
The following action has been taken by the health board:
All non-urgent outpatient clinics will be postponed – this includes face to face and virtual.
All non-urgent planned surgery will be postponed.
All specialist nurse clinics will be postponed.
All non-urgent diagnostic services (e.g. radiology/endoscopy) will be postponed.
Urgent cancer services and clinically urgent patients will continue to be seen
There are 419 suspected, confirmed or recovering Covid-19 patients in Cwm Taf Morgannwg hospitals and the health board say their intensive care beds are near capacity.
There are a further 50 patients in their temporary hospital Ysbyty’r Seren and many health and social care staff are off work with Covid-19.
The coronavirus case rate in Merthyr Tydfil is the highest in the UK with the seven-day rolling figure as high as 1,032 per 100,000 people.