Running for over 160 years, the organisers were expecting more than 215,000 people on course.
Fashion in the Field winners are expected to be announed this afternoon.
This year, the competition will be judged by five festive fashionistas - the biggest judging panel in its history.
Wilhelmina Shrimpton will keep the crowd informed throughout the competition as judges, Sarah Stuart (head of styling at Newshub), celebrity stylist Lulu Wilcox, 2017 Viva Prix de Fashion winner and Beauty by Hannah's Hannah Carson, Showroom 22's Murray Bevan and leading menswear buyer, Christian Harmes, work out their best dressed.
The awards include: best dressed woman (1st, 2nd and 3rd), best dressed man (1st, 2nd & 3rd) and the millinery award.
Prizes include Hawaiian Airlines air miles, SkyCity packages, Balmain sunglasses, Barkers gifts and Champagne Mumm prize packages.
The best dressed woman will also win a weekend away in a Hyundai Tucson and gain automatic entry into the Regional Final of Viva Prix de Fashion - the national fashions in the field final - held on Vodafone Derby Day in March.
A new precuinct, the Paddock, is a more relaxed space for eventgoers with no dress code. There is all-day music from Jupiter Project, Mac Mylo (The Black Club) and international DJ/songwriter Arii Jade.
Punters not letting rain get to them
Heavy gray clouds and a stifling humidity are hanging over the Boxing Day races at Ellerslie this afternoon but punters aren't letting the threat of rain put a damper on their day.
Thousands of race goers are packing the race course out today, dressed to impress and for the most part behaving themselves.
Security guard Ken Wolgramm is working his first Boxing Day at the races and said a few people had to be booted out of the venue for drunken behaviour quite early in the day.
"But apart from that it looks like everyone's having a good time," he said.
He's keeping an eye on festivities this afternoon to make sure everyone behaves - and putting a bet on here and there in between.
Pauline Hedburn and Judy Maynard got here just before the first race and had reason to be early.
They've got shares in two horses: Embellish and Gris Dame.
Dressed in a white shirt with a flamingo design on his tie, jacket and shorts, Hooper was getting into the spirit of the day.
Among his similarly brightly dressed friends were William Furness in a yellow and black Batman suit, Joe Redshaw in a suit decorated with ice blocks, and not one but two mates dressed as Santa.
Peter Davey has been coming to the Boxing Day races for six years.
Every year he changes his outfit to keep thing fresh, but his signatures stay the same: cap, glasses, and metallic glam.
"I have a bit of a look but I try to change [it up]," he said.
This year he's come with his friend Maria Hoyle, who is similarly sparkling.