A young girl has been tragically killed at a horse riding event in Sydney.

The nation’s hearts collectively broke two months ago when 17-year-old Olivia Inglis fatally fell from her horse at a horse trials event in the Hunter Valley.

Now, tragically, a second teen has died after falling from her horse while competing in the Sydney International Horse Trials at Horsley Park this morning.

Caitlyn Fischer, a 19-year-old Bairnsdale, Victoria native, was riding in the cross-country event when the incident occured.

A police investigation is underway and the trials have been cancelled after the accident happened at 10:40am this morning at fence two of the race course.

"On behalf of the whole sport I would like to extend our deepest sympathy to Caitlyn's parents Alissa Carr and Mark Fischer and her family. The thoughts and prayers of horse people all over the country are with Caitlyn's family and friends at this sad time," Equestrian Australia chairwoman Judy Fasher said in a statement.

It is unclear of the injuries sustained by the teen, who worked for elite equestrian Christine Bates, all that is known is she was fatally injured after falling off her horse, Ralphie.

Fischer was provided with medical care from a paramedic at the scene but could not be revived.

Our thoughts are with her friends and family at this terrible time.