At Wellington Hospital, nine people were treated during a period that was slightly busier than a standard weekend.
But the patients included four teenagers, two of whom were under the legal drinking age.
"The Emergency Department team said it was concerning to see underage people coming in drunk," spokeswoman Vikki Carter said.
Tauranga Hospital clinical director Dr Derek Sage, who worked both this and last New Year's Eve shifts, said the hospital received 57 patients in the eight hours after midnight, which made for a "heavy night" and busier than last year.
"That though is in line with our increasingly higher average number of daily presentations," he said.
"If you go back a few years, in 2002 we would have expected around 90 to 115 patients a day, now that range is consistently around 140 to 160."
Tauranga Hospital ED had 175 presentations on New Year's Eve and 126 up to 4pm on New Year's Day.
Dr Sage said the overnight presentations were mostly alcohol or drug related, with patients predominantly in the 15-30 age group, and the first presentations of the evening started around 9.30pm.
"There was a high percentage of out-of-towners boosting the numbers."
Hospital staff had done a "superb job" under high pressure, he said.
Waikato Hospital Emergency Department clinical director Dr John Bonning said his ED had also been "extraordinarily busy" since Christmas, with total patient numbers up 15 to 20 per cent on what was expected.
With the surge came higher numbers of drunken patients, making an already busy time even more challenging for under-pressure doctors and nurses.
"Emergency departments are really under-staffed at the best of times," said Ian Powell, executive director of the Association of Salaried Medical Specialists.
"So when you add an extra alcohol component to it, you increase the pressure, by a small number of people, on what is an already over-stretched workforce."
Dr Bonning said an average 8 per cent of all presentations to emergency departments had alcohol involved and, at peak times, that figure rose to about 12 per cent.
"So if we get 200 presentations in a 24-hour period like New Year's Eve, it was likely 25 people were there as a result of alcohol.
"And these drunk people are very, very challenging -- they can hide significant injury, they can vomit everywhere, and they can be obnoxious and not very co-operative."
He appealed to revellers to drink in moderation and save themselves -- and his staff -- an unplanned trip to hospital.
"If you are going to have a few drinks, plan it, drink sensibly, know when you are going to stop and when you've had enough, and don't get behind the wheel of a car or get into a fight -- it's really quite simple."