Extra ambulances, paramedics and emergency call centre staff will be on hand across the country tonight to cope with the throngs of people seeing in 2015.
St John New Zealand is expecting triple its usual number of calls - more than 600 - in the four hours from 10pm to 2am.
Ninety-one extra ambulances will be on the roads along with about 180 extra front-line staff in key hotspots like Auckland, Christchurch, Mt Maunganui, Queenstown and Gisborne.
The ambulance service said the "crucial hours" were the ones either side of midnight.
St John assistant operations director Derek Liefting said the service was expecting such a big response that it had activated its National Ambulance Emergency Operations Centre in Auckland.
Use of the centre is usually reserved for major incidents or big sporting events like the cricket and rugby world cups.
"That way we keep an eye out on what's happening out there, particularly with road closures, major incidents and weather too," Mr Liefting said.
"We also have to think about helicopter responses in the rural areas particularly if the weather was going to be bad in the South Island."
Most of the extra cases St John dealt with around New Year's Eve could be attributed to alcohol, Mr Liefting said. Incidents could include unconsciousness, assaults including sexual assaults, fights and stabbings, other illnesses, and falls.
St John had been able to put data together from the last five years to predict what was likely to happen tonight, which had helped with planning.
"Having the data from previous years and just seeing when the incidents come, and where, we can post resources to suit that demand."
Wellington's ambulance service also preparing
Extra ambulances and staff will also be on hand in and around Wellington for tonight's New Year's Eve celebrations.
Wellington Free Ambulance is expecting callouts to increase from 9pm tonight through to 4am tomorrow.
The ambulance service dealt with 165 incidents over 24 hours last year but said New Year's Eve had gone smoothly for it in recent years.
Its executive manager of service delivery, Andy Long, still said tonight would be one of the year's busiest nights.
"We've got three additional ambulances on duty tonight, that's over and above our normal ambulances resources which are fifteen at any given time.
"We have two additional call takers on duty in the 111 call centre and an additional manager, and an additional manager on duty in the field of operations."
Mr Long said people should see in the new year safely and responsibly.
"Usually people who celebrate hard are one of the issues we have so we always encourage people to enjoy seeing in the new year but do it safely and responsibly," he said.
"We do get increased numbers of illnesses - people still do suffer from heart attacks and the like."
New Year's Eve tips from Wellington Free Ambulance
- Drink responsibly and look after your friends.
- Follow the sun-smart rules of slip, slop, slap and wrap.
- Carry water with you and take regular drinks to keep hydrated.
- Keep an eye on the children, especially around water.
- Be super safe on the road.
- If you are going to drink, have a plan to get home - whether that means a sober driver, taxi or public transport.