A man has died after crashing his mountain bike in Daisy Hill forest in Brisbane's south.

Other mountain bike riders found the 52-year-old man unconscious at the bottom of a very steep trail in the conservation park about 8am on Monday.

Daisy Hill Conversation Park in Brisbane's south is considered one of Australia's premier mountain biking areas.

The man, from Wellington Point, was taken to Princess Alexandra Hospital by ambulance with critical head injuries, but passed away about 9pm.

Police said it appeared the man had lost control of his bike while riding, but they would continue to investigate the circumstances surrounding the incident.