Billionaire Gina Rinehart has made a rare wrong step, tumbling down the stairs of a Melbourne Cup marquee.

Australia's richest woman was heading down the stairs at the Emirates marquee at Flemington on Melbourne Cup day when she stumbled.

Former federal MP Sophie Mirabella and now Rinehart employee was one of many nearby lending a hand to get the 62-year-old mining magnate quickly back to her feet.

Earlier in the day, Ms Rinehart entered the same marquee closely flanked by security and a mass of photographers.

Asked for her best bet, the billionaire said she doesn't gamble but offered a tip.

"Let's back our Australian horses," she told AAP.

She was onto a winner of sorts, with German-bred Australian-trained Almandin saluting in the $6.2 million dollar handicap.