One of Australia's top female jockeys has been trampled to death in a horror fall that has sent shockwaves through the horse-racing world.

Simone Montgomerie was thrown to the turf at more than 40mph during a build-up race to the iconic Darwin Cup at Fannie Bay racecourse, in the Northern Territory, today. She was 26.

Stewards are investigating the cause of the tragedy, but early indications suggest the mother-of-one's saddle may have slipped, sending her under the hooves of the stampede, just 100m from the finish.

Medics rushed onto the course to treat her but she died of her injuries soon after arriving at hospital.

Ms Montgomerie, who was aboard Riahgrand in the sprint, was well-known on Australia's horse-racing scene and was a popular member of its close-knit jockey fraternity.

Other jockeys were left in a state of visible distress when news of their friend's death filtered through the course forcing organisers to cancel the remaining races, including the Darwin Cup itself.

Darwin Turf Club chairman Brett Dixon said: 'As far as we are concerned, Simone was our family and we are all devastated by this accident.'

Jockey Kerrin McEvoy, who won the 2000 Melbourne Cup aboard Brew, told news.com.au: 'I'm shattered by the news.

'I know Simone really well, we actually did pony club together. My condolences go to the Montgomerie family. She's a beautiful girl, it's just a tragedy.'

Former Grand National winner and Channel 4 racing pundit Mick Fitzgerald tweeted: 'Thoughts go out to the family of Simone Montgomerie who died earlier today following a fall at Darwin cup meeting.'

Horse racing is one of the few 'mixed' sports where men and women compete head to head.

Nevertheless, professional female jockeys are comparatively few, so those who do make the top flight are held in particularly high regard.

Ms Montgomerie started her riding career in South Australia before moving to Darwin in November 2009 after joining trainer Michael Hickmott's stable. 

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Last season, she finished fourth in the Northern Territory Jockeys Premiership after riding 27 winners, beating another woman, Felicia Bergstrand, by three.

Just last week she said of that achievement: 'This was not something I ever thought about achieving, but when it comes it is a bonus.'

Montgomerie is the daughter of Peter Montgomerie, who trained 2005 Melbourne Cup runner-up On A Jeune.

National Jockeys' Asscociation general manager Des O'Keeffe told the Herald Sun: 'It is unbelievable that this has happened just two days after National Jockeys Celebration day around the country.

'I have had many jockeys ring me and they are absolutely shattered.'

National Jockeys Celebration day was held on Saturday by the National Jockeys Trust which provides support for families of killed and injured jockeys.

Before news of Ms Montgomerie's death had reached the course, Chief Steward Lindsay Lane said: 'Obviously there's been quite a serious fall and Simone Montgomerie has gone to hospital in a critical condition.

'The stewards are somewhat concerned given the close nature of the riding community here in Darwin about the effect that it may have on the other riders so we've spoken to the riders.

'Some of them are quite concerned and quite upset so we've taken the view that the number one priority is safety and wellbeing of the riding group and we've elected to abandon the meeting.

'I'm sure that the riders can ride at their best but whether they can ride safely with the fall on their mind, the stewards aren't totally convinced.

'The common sense thing to do is to call the meeting off. It's very unfortunate for the club.'