Staff at Altnagelvin Hospital in Derry have taken to the picket line in a protest over pay.
They are among thousands of NHS workers in the North who staging a four-hour strike.
Members of the Unite and GMB unions began their action at 8.00am this morning. They will return to work at 12.00 noon.
Paramedics and midwives are among those taking part in the strike.
Unions say emergency services would not be affected.
Unions want a recommended one per cent pay rise to be implemented for all staff, but the National Health Service said this would cost too much.
