A chilly day of hail and rain in Melbourne hasn't been enough to deter thousands of racegoers pouring into the Flemington Racecourse for the biggest day on Australia's racing calendar.

Crowds were banned from the 2020 Melbourne Cup, while the 2021 race was capped at 10,000 people due to COVID.

Melbourne-Cup winning jockey Mark Zahra has described the "miracle" moment he rode Gold Trip to victory.

The winning stallion was trained by Ciaron Maher and David Eustace.

This morning, attendee Leanne Clinch said rain would not put a dampener on the day.

"I'm looking forward to the fashions and seeing everyone out and having a good time," she said.

"I don't think [the rain] will matter, because we'll be inside, sipping champagne."

Sharon Polson agreed the weather wouldn't stop the pair from having a good time.

"I never let the weather deter me."

The last time Flemington was open to all crowds on Cup Day was in 2019, when 81,458 people came to the track.

More than 71,000 people attended Victoria Derby Day on Saturday, and a crowd of 80,000 was expected today.

The celebrations today came as Victoria Police confirmed they were investigating an act of vandalism on the racecourse.

Police said the course was broken into about 6am and that vandals had poured an "unknown substance" onto the track.

Vision on social media showed a hose pumping a black sludge over the course.

A Racing Club Victoria spokesperson said only "minor damage" was caused after fluid was poured onto the track near the 1,500-metre area.

The track was immediately cleaned before stewards judged it safe for racing to occur without any impact, the spokesperson said.

Forecasted wind and rain begins

At around midday, rain and wind forecasted by the Bureau of Meteorology began, leading to the track's rating being downgraded.

Bureau of Meteorology forecaster Chris Godfred said the rain was likely to continue through the afternoon.

"Melbourne is expecting a top of only 14 [degrees Celsius] for Cup day, so very chilly, and on top of that there will also be quite frequent showers," Mr Godfred said.

"We are — with the cold front — looking at the risk of some thunder and some local small hail, especially during the afternoon."

This morning, Todd Anthony said he brought an umbrella which "sparkles like my shoes".

"I'm over the moon because the sun is shining and I got to wear glitter today," he said.

"I love the horses, but when I come here I generally don't see them because I'm hanging out in the Myer Fashions on the Field section which is my favourite place."

Joel Parkinson dressed the part.

"It's Melbourne Cup day — it's about bright, bold colours — you've gotta commit to the brief."

Melina Bagnato was enjoying the opportunity to dress up after years of sporadic lockdowns.

"It's a great excuse to go above and beyond," she said this morning.

It was the first Melbourne Cup for Cara and Scott Connor, who drove for more than five hours from Griffith in New South Wales to make it.

Ms Connor said she was taking the opportunity to show off the skills of a local hatmaker in Griffith.

"We're really enjoying our day today," Ms Connor said.

Gold Trip snatches Cup victory

Trainers Maher and Eustace achieved their first Melbourne Cup victory with Zahra riding Gold Trip home at Flemington.

Second was the Geelong Cup winner, Emissary, followed by Bendigo Cup winner, High Emocean.

The Melbourne Cup win represents a first for jockey Zahra, as well as for the trainers.

Meanwhile, Irish stallion Interpretation failed to finish the race, but has since been described as "OK", having avoided significant injury.

The prize pool for the Melbourne Cup is $8.075 million. This includes $7.75 million in cash and a number of trophies worth a total of $325,000.

Three per cent of all prize money is deducted and directed to equine and jockey welfare.