Norfolk hospitals have "robust plans in place" for dealing with a doctors' strike, although patients may face delays.
Junior doctors are walking out from 7am on Monday, March 13 until 7am on Thursday, March 16.
Some 40,000 are set to take part in the stoppage, which has been called by the British Medical Association over pay.
Both the Norfolk and Norwich University Hospital and the Queen Elizabeth Hospital in King's Lynn issued a statement saying: "Our primary focus on these strike days is to maintain services for patients who need emergency and life preserving care.
"We have robust plans to deal with a range of disruptions and our senior doctors will be providing cover to maintain urgent and emergency services.
"During industrial action, we will need to reduce the number of appointments we have planned at our trust.
"We are contacting patients directly if this means that their appointment will need to be postponed.
"We understand how disappointing and concerning this will be for those waiting for treatment and we are very sorry this is the case."
The James Paget Hospital said: "James Paget Hospital remains open during this period, and patients that need urgent or emergency care will continue to receive the treatment they need, when they need it - but those in less urgent need of care may experience longer waiting times than normal."
The 72-hour strike is expected to have a bigger impact than any action by health unions since December, with junior doctors across England expected to withdraw from A&E departments, cancer care, maternity, and planned care.
Writing in the Telegraph, health secretary Steve Barclay warned the action posed "a real risk to patient safety, which should pose difficult ethical dilemmas for our hard-working junior doctors”.
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