Nurses in England, Wales and Northern Ireland have started a second day of strike action this morning.
Staff from the Royal Cornwall Hospitals Trust, Cornwall Partnership Foundation Trust and South West Ambulance Service all voted to be part of the industrial action.
Staff in Cornwall will not be involved in the action today. The union, the Royal College of Nursing, says the county is part of "phase two" of the action.
However, the RCN previously confirmed nurses at Derriford Hospital in Plymouth, where many patients from Cornwall are cared for, will take part in the industrial action.
Staff will continue to provide "life-preserving" and some urgent care but routine surgery and other planned treatment is likely to be disrupted.
Advice has been issued for people during the action:
People who are seriously ill or injured, and whose life is at risk, should call 999 as usual, or call 111 for non-urgent care.
Other services, such as some cancer treatments, mental health services or urgent testing, may be partially staffed.
More routine care is likely to be badly affected, including planned operations such as knee and hip replacements, community nursing services and health visiting.
Official advice is that anyone with an appointment which hasn't already been rearranged should turn up at their allotted time.
GPs, community pharmacies and dentists will not be affected.