Plymouth's Derriford Hospital says it was forced to call in staff from home following massive demand.
Nearly 600 patients turned up at the casualty unit last weekend.
Some reported waiting more than five hours before being attended to.
Director Lee Budge says it was a "very challenging weekend on top of an extremely busy week".
"On Saturday 291 patients attended our Emergency Department including a number of major trauma patients and on Sunday 286 people attended. These numbers do not include people who attended our Minor Injuries Units in the Cumberland Centre, at Tavistock and Kingsbridge.
“Additional staff were called in to cope with these pressures and both our clinical and non-clinical teams pulled together magnificently to ensure patients received the best possible care.
“We are truly blessed to have so many dedicated, talented and caring people to look after our patients and I can't thank them enough for the professional way in which they responded.”