Bones in Royal National Park could have been there months

Police say bones found close to a road in the Royal National Park on Saturday could have been there for months, if not years.

The homicide squad is investigating after the discovery was made Sydney’s south by a motorist who stopped for a bathroom break on the quiet stretch of bush.

Officers were called to Sir Bertram Stevens Drive in the Royal National Park on after bones were found at the bottom of a ravine just before 5pm.

Police later confirmed the bones were human, but so far can only say they belong to an adult, rather than a child.

"The homicide squad is now assisting Sutherland police with their investigation," a NSW Police spokesperson told 9NEWS.

The remains have been sent for DNA testing and a post mortem and initial results could be confirmed as early as this week.

Police are continuing to gather evidence at the site and believe the death could be suspicious.

Anyone with information is urged to contact Crimestoppers on 1800 333 000.