People showing up at Wellington's emergency department are being told to expect longer waits, as high patient numbers push the hospital's capacity.
The hospital said it had been more than 93 percent full for the past month, and more people were going to the emergency department than usual.
Chief medical officer John Tait said there was no single reason the hospital was busier, but staff had noticed people were generally more unwell when they went to the emergency department and they needed to be admitted.
Mr Tait said, because of the high numbers, people with non-urgent illnesses or injuries were having to wait longer than usual.
He said people should get the flu vaccination, and visit their GP if they were unwell, as it might stop them from needing to go to the hospital.