Tens of thousands of nurses are going on strike for the first time across England, Wales and Northern Ireland.
Picket lines are being set up at dozens of hospitals in a dispute over pay, with the Welsh Government saying services will be “significantly impacted”.
Thousands of NHS appointments and operations have been cancelled because of the strike, with the health service running a bank holiday-style service in many areas.
The Royal College of Nursing (RCN) has said it will still staff chemotherapy, emergency cancer services, dialysis, critical care units, neonatal and paediatric intensive care.
Some areas of mental health and learning disability and autism services are also exempt, while trusts have been told they can request staffing for specific clinical needs.
When it comes to adult A&E and urgent care, nurses will work Christmas Day-style rotas.
Saffron Cordery, interim chief executive of NHS Providers, told the PA news agency NHS trusts were “pulling out all the stops” to lessen the impact on patients.
She said: “The picture will vary across the country as trust leaders work out service levels with unions locally.
“But it’s inevitable that some operations or appointments will have to be rescheduled and trusts are pulling out all the stops to minimise disruption.
“The cold snap has ramped up demand that was already at or close to record levels, but on strike day NHS trusts will do everything they can to ensure that essential services are properly staffed and patient safety, always the number one priority, is safeguarded.”
RCN chief executive Pat Cullen has accused Health Secretary Steve Barclay of “belligerence” after he refused to discuss the issue of pay.
He has repeatedly said the Government is sticking to the recommendations of the independent pay review body, which said nurses should get a pay rise of around £1,400.
The RCN has been calling for a pay rise at 5 per cent above inflation, though it has indicated it would accept a lower offer.
When it submitted the 5 per cent figure to the independent pay review body in March, inflation was running at 7.5 per cent.
But inflation has since soared, with RPI standing at 14.2 per cent in September.
Several trusts have already given details of cancelled outpatient appointments and planned treatments.
The Western Trust in Northern Ireland said it had “regrettably taken the decision to cancel some non-emergency services”, with 587 outpatient appointments postponed across Altnagelvin Hospital, Omagh Primary Care and Treatment Centre and South West Acute Hospital.
Some eight planned inpatient and day case procedures have also been cancelled.
The trust said there would also be reduced staffing in community nursing services including rapid response nursing, district nursing, community respiratory nursing and continence services.
