Christchurch's only 24-hour GP surgery was forced to close its doors for almost three hours on Tuesday night due to high demand.
In a statement, Pegasus Health said its Madras Street urgent care facility was full and it felt it was clinically unsafe to accept new patients until the number of people waiting to be seen reduced.
The surgery closed just after 9pm until 11.45pm.
Pegasus Health general manager for patient and provider services Lisa Brennan said patients were provided with information about where to seek care until the surgery returned to normal operating.
"We worked with other providers and Christchurch Hospital Emergency Department to ensure those who needed care immediately were able to be seen."
She said it was the first time high demand had closed the 24-hour surgery.
"It was the best way to ensure we were providing safe quality care and will remain an option while patient numbers remain high."
The Nurses Organisation (NZNO) said members at the surgery had "been given a directive by the employer not to speak publicly about the temporary closure".
"Our members have for some time anticipated the sort of closure that happened last night," it said in a statement.
"It is a sign as how bad the nursing crisis has become. Primary health faces a nursing crisis, as does the wider sector. Staffing levels are woefully inadequate.
"This is why NZNO is calling for more nurses as part of our Maranga Mai! campaign.
"We are also seeking parity in terms and conditions for all nurses so that we don't see nurses leaving primary health or aged care to go to Te Whatu Ora because the pay is higher," NZNO said.
"The primary health care sector is treated in an inferior way to nurses at Te Whatu Ora and due to this nurses will continue to leave and staffing will only get worse."
Aged Concern Canterbury said health care staff were working extremely hard to keep delivering services with minimal disruption, despite the immense pressure on the system.
Chief executive Greta Bond said it was important people kept seeking help if they need it.
"Sometimes older people will hesitate to seek medical help if they feel that the system is under pressure.
"I would really encourage people not to assume that they are better off or others are worse off - they should seek help when it's needed and not wait until it's too late."