As 3000 shots of fireworks were fired off from Auckland's Sky Tower to welcome 2018, the country also welcomed the first baby of the new year.

The healthy baby boy, weighing 3.5kg, was born at Auckland Hospital at 12.01am to a Howick couple on the first day of the new year.

There are 526,600 minutes in a year, meaning the odds of giving birth at 12.01 on January 1 are one in 526,600.

Proud dad Chien Cheng Lu and mother, Ena Lu, both 32, have named their precious bundle Rex — which has nothing to do with being a new year baby, but because they say he looked like a T-Rex at his first ultrasound.

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The baby was born on his due date, but had to be induced because mum has gestational diabetes.

"It's been incredible actually, I've been told that only 2 per cent of people actually deliver on their due date," said Ena Lu, a commercial analyst.

"Everyone in my family is like 'wow', surprised and excited as well. It's the first grandchild for my husband's side of the family, so we're all pretty excited."

Lu, originally from Hong Kong, said her Taiwanese father-in-law had just arrived in New Zealand and would be deciding the baby's Chinese name.

"The name needs be based on when they are born, and that will determine what [Chinese] characters are used in the name," she said.

She said it was a long labour, having arrived at hospital at 7.30pm on New Year's Eve, but looked to be in good health and spirits after welcoming her first born.

Meanwhile, 18-year-old Kimberley Thomas ditched the usual New Year's Eve parties for the maternity ward to deliver the country's first baby girl.

Baby Kya Thomas-van Luit, weighing 3.3kg, was born at 12.15am at west Auckland's Waitakere Hospital.

18-year-old Kimberley Thomas holds Kya Thomas-van Luit who was born at 12.13am on New Years day at Waitakere Hospital, making her the youngest new mother this year. Photo / Greg Bowker
18-year-old Kimberley Thomas holds Kya Thomas-van Luit who was born at 12.13am on New Years day at Waitakere Hospital, making her the youngest new mother this year. Photo / Greg Bowker

"My due date was the 31st, but this still came as a huge surprise," Thomas said.

"I was having really strong contractions and then as soon as I hopped out of the car, my waters broke. I had to come inside and was pushed in straight away, it was so quick."

Thomas said it was an "interesting way" to spend New Year's, and one that she'll never forget.

"Everyone else is out partying, and here I am having a baby," she said.

"But I guess it's really special to have a new year baby, and something that family and friends will certainly talk about."

Grandmother Rachel Krum said she was on holiday in Taupo, and rushed back when she got the news.

"It really came as a surprise...but it's exciting times for all of us," Krum said.