All eyes are on the second year favourite Vauban. The horse fell short in last year's cup, but has returned and topped the odds again.
A spokesperson for the betting agency, Thad Taylor, told Morning Report in the 10 minutes leading up to the Cup the TAB expected to sell about 7000 bets a minute.
He recommended that people place their bets early to avoid missing out.
"But you know some people like to wait, like to get as much information as they can, listen to a few people in the office - 'what have you got to say' - and they wait late."
The second-biggest day for the TAB was New Zealand Cup Day at Addington, which generally took in about $15,000 in bets, he said.
In terms of the betting Melbourne Cup Day "dwarfs all other days still", he said.
"I mean New Zealand trotting cup is obviously significant for us and still a very very big day but there's no doubt it will run a very distant second to the Melbourne Cup in terms of interest, turnover and all that goes with it."
In terms of where people were placing their bets, Taylor said the Europeans dominated the landscape with the likes of Vauban and Absurd.
"And then two horses that have had lead-up races in Australia, one Smooth Operator won the Geelong Cup, he's trained by Bryan Allison, he was very good. And Seed King the other day won the Bendigo Cup, it's another European-trained runner that'll be right in commission in the race."
There were three New Zealand-trained horses in the race, but all were long-shots, he said.
"We're a patriotic bunch, so I can tell you if a New Zealand-trained runner does win the Melbourne Cup it'll be a terrible result for the New Zealand TAB because Kiwis love backing Kiwis."
Racing commentator Aidan Rodley said Sharp 'N' Smart, who was trained in Hamilton by Graeme and Debbie Rogerson, was the best Kiwi chance.
"This horse has won three group one, so that's a top echelon of races. His only start at Flemington was two years ago where he ran second in a Victorian derby and he ran really well in the Moonee Valley Cup this third last time out."
Another New Zealand-trained horse was Positivity trained by Andrew Forsman, he said.
"She just had a bit of a bruised heel leading into her last start so she lost a bit of work, her conditioning wasn't right, but she's come on really well since then ... and she looks in great order."
Trust in You, trained by Bruce Wallace and Grant Cooksley, ran sixth in the Auckland Cup last year and has been recently been running well in Sydney, he said.
There had not been three Kiwi-trained horses in the race since 2009, and the last New Zealand-owned and trained winner was in 2001, he said.
The Melbourne Cup attracts a huge amount of interest and was likely to get an even bigger crowd than Derby Day at Flemington which was on Saturday and attracted a crowd of 81,000, he said.
"The Melbourne Cup is just the race that grips people, it's the biggest wagering race in Australia but also in New Zealand."
The race begins at 5pm today.
