St John declared a 'major incident' on Monday night caused by delays in transferring patients to Waikato Hospital.
The declaration allows arrangements to be made to ensure its ambulance service can continue.
St John said it worked with hospital staff at 10.30pm to set up an ambulance waiting area where they offloaded patients to an area managed by a nurse.
It said it prioritised patients in most urgent need to get to the emergency department, while ensuring those waiting in ambulances received appropriate care and observation.
Te Whatu Ora Waikato said it was at 103 percent occupancy on Monday with 143 patients in its ED at 6pm, one of the busiest periods it has experienced.
Interim lead hospital and specialist services Michelle Sutherland said extra doctors were deployed to assist the flow of patients.
"This meant that ambulances could urgently offload any transported patients into the ED if they had two or more priority community response calls in the central Hamilton area however, this capability was not required. Normal services were maintained throughout," Sutherland said.
"Work is continuing towards reducing the high levels of demand on our EDs."
Hato Hone St John general manager ambulance operations Debra Larsen said any delay was not ideal for patients and their whānau.
"We maintain that the safest outcome is for all patients to be transferred into the care of hospital staff as soon as possible."
Earlier this month, a provisional improvement notice was issued to Waikato Hospital's emergency department after concerns about unsafe staffing levels.
That followed another 'major incident' being declared by St John on Monday 31 July after ambulances had to wait with patients at the hospital for a record number of hours.