Auckland's Middlemore Hospital is filled to capacity and can't take in any non-emergency patients.
It has issued a warning to general practitioners in the area, telling them not to refer patients directly to hospital and instead consult with specialists.
However, emergency services are unaffected.
It is a common occurrence, and the hospital fills up 30 to 40 times every year, a Counties Manukau DHB spokesperson said.
Hospital staff are working tirelessly to ensure patient care isn't affected, and that those who need treatment are getting it, she said.