The 50-year-old was stopped by Customs officers at Sydney Airport on Thursday to have her luggage examined after arriving.

Customs said the scan of the Cambodian-Australia woman's luggage detected ephedrine and cocaine residue which prompted a body scan.

The body scan images "showed inconsistencies", Customs alleges.

The Australian Federal Police then took the woman to hospital where she allegedly later passed 252 pellets.

"Initial testing indicated the pellets contained heroin, with further testing to take place to determine the exact weight and purity," a statement from Customs said.

Australian Customs and Border Protection Service's regional Commander Tim Fitzgerald said "this method of importation was particularly concerning".

"The potential danger this woman has put herself in is a reminder of the risks involved with this kind of concealment," Mr Fitzgerald said.

"It is also a reminder to the Australian public of the lengths that people and organised criminal groups will go to in order to import illicit drugs into our country."

The woman has been charged with one count of importing a marketable quantity of heroin and will appear in Sydney's Central Local Court on Thursday.