Police in North Carolina have confirmed that a prosthetic leg found last week belongs to missing Australian girl Zahra Baker.

Ten-year-old Zahra Baker was reported missing over three weeks ago in the town of Hickory, North Carolina.

Zahra is a bone cancer survivor and had part of her left leg amputated.

Police found a prosthetic limb in the bush last Tuesday several kilometres from where her family lived.

They have since confirmed the serial numbers match one fitted to Zahra in Australia.

Her American stepmother is in jail facing an obstruction of justice charge after she admitted to writing a false ransom note on the day Zahra was reported missing.

Her Australian father has been released on a bond but is facing other unrelated charges.

Zahra moved with her father from Townsville in north Queensland to North Carolina and was being home-schooled.

The police search for her continues.