Caitlyn Jenner's longtime friend and manager Sophia Hutchins has died, aged 29.

Sophia Hutchins, Caitlyn Jenner's manager and friend of a decade, has died in an all-terrain vehicle (ATV) accident in Malibu, California, near Jenner's home.

She was 29.

According to TMZ, Hutchins was declared dead at the scene on Wednesday morning, US time. The outlet reported she was riding the ATV on the road where Jenner lived, when she struck the bumper of a moving car. Her vehicle was forced off the road and plummeted 350 feet (107 metres) into a ravine.

The two passengers in the car were uninjured.

TMZ has reached out to Jenner. It's unknown whether she was home at the time of the incident.

Hutchins and Jenner met in 2015, shortly after Jenner publicly announced her transition. Hutchins, who is also transgender, was a former CEO and director of the Caitlyn Jenner Foundation.

Sophia Hutchins in 2019. Image: Getty.

Hutchins appeared in several episodes of the E! docuseries I Am Cait.

She was born April 1, 1996 in Bellevue, Washington. In her Instagram bio, she describes herself as a serial entrepreneur, founder and investor. She founded health technology company LUMASOL.

Jenner described Hutchins as her "best friend, family and confidant" in a 2018 interview with The New York Times.

"She is one of the top minds in her field," Jenner said.

"Her value in my life is undeniable. The sky is the limit with her entrepreneurial spirit."

Feature image: Getty.