Junior doctors at Sunderland Royal Hospital have begun a strike in opposition to proposed new Government contracts.
The doctors are providing emergency cover only during the 24-hour walkout, which got under way at 8am.
The Government says the changes are needed to create more seven-days services, but the British Medical Association warns safeguards to keep a lid on excessive hours are being weakened.
Bosses at the Royal say one operation has had to be cancelled with more than 60 outpatient appointments rescheduled.
BMA rep Alex Thompson, a junior doctor at the Royal, said: "I think it's a real shame that we have had to do this but when 98% of doctors are saying there is a problem with the contract, the Government should be listening to us.
"We would love to provide a seven-day service, but without extra people we are going to struggle.
"I hope that the Government listen, understand that we have been forced into this and come back to the table and negotiate with the BMA."
A spokeswoman for City Hospitals Sunderland NHS Foundation Trust said: "We can confirm one elective operation and approximately 65 outpatient appointments have been rescheduled as a result of the junior doctor industrial action today.
"We do have some junior doctors working today to help ensure we have been able to provide an emergency service and apologise to those patients who have been affected."