US authorities are working to determine if skeletal remains, reportedly including a skull, found off a highway in North Carolina are those of murdered Australian girl Zahra Baker.

Local television stations in Charlotte, North Carolina, said the Caldwell County Sheriff's Office was called to a wooded area on Tuesday afternoon after the skeletal remains were found about a kilometre from US Highway 268.

NewsChannel 36 said deputies were trying to identify the remains and how long they had been in the wooded area, which had not been searched after 10-year-old Zahra disappeared in 2010.

Agents from the Federal Bureau of Investigation, Hickory Police Department and State Medical Examiner's Office are on scene, WBTV reports.

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Sources have said it was believed a skull was among the remains.

When asked if the remains could be those of Zahra Baker, a source told WBTV it is "crossing their minds".

Some of Zahra's remains, including her prosthetic leg but not a skull, were recovered near where she lived in Hickory in North Carolina with her father and step-mother.

Zahra's stepmother, Elisa Baker, pled guilty in September to second degree murder and was given an 18-year prison sentence.

Her father, Adam Baker, who has since returned to Australia, was not charged over the death of his daughter but does still face several unrelated misdemeanors and two felonies.

-AAP