A teenage boy has been choked to death in a motorcycle accident on the NSW Central Coast, police say.

A passer-by raised the alarm about 11.30am today when he found the 17-year-old boy lying dead on a fire trail off Katara Road, at Warnervale.

Investigators believe a rope he was carrying across his shoulder became caught in the motorcycle chain and tightened around his neck, choking him to death.