The trio - a 15-year-old boy who cannot be named for legal reasons, 18-year-old Rachel Ann Diaz and 21-year-old Hutchinson Tran -- have pleaded guilty to drug trafficking charges involving one kilogram of heroin (2.2 pounds).

They were due to appear in Hong Kong's High Court before Deputy Judge Peter Longley at 10:30am (0230 GMT) but the court clerk said he would delay proceedings to 11:30am.

The maximum penalty for trafficking is 20 years in jail.

The three have been in custody in this southern Chinese territory since they were arrested April 12 last year after police raided their low-budget hotel room in the Tsim Sha Tsui district.

They discovered the drug in 114 condoms and several glove fingers that they say the two teenagers were to swallow before boarding a flight to Sydney.

Media reports suggested the two juveniles had been recruited as "mules" to smuggle the drug worth an estimated one million Australian dollars (US$ 720,000). Tran allegedly set up the deal on behalf of a Sydney-based gang and supplied the heroin for them to swallow.

Prosecutors said Diaz and the minor had been promised AS$ 200 by a drug syndicate for each five-centimetre packet of heroin they swallowed.     

They had been under surveillance as a result of a joint police operation to stop the use of drug mules to smuggle heroin from Hong Kong to Western markets.

According to Australian press reports, Diaz, a Filipino-Australian, was a trainee hairdresser in Sydney and the 15-year-old boy, a Vietnamese-Australian, used to work at a McDonald's.

Diaz's father has previously flown to Hong Kong to support his daughter at her trial.