A 73-year-old Australian citizen has been sentenced to death in Vietnam for heroin trafficking, according to local media.

Nguyen Thi Huong was arrested two years ago trying to board a flight to Australia with 1.6 kilograms of heroin hidden inside 36 bars of soap in her luggage.

Huong said a woman gave her the soap and she did not know it contained heroin, but a Ho Chi Minh City court rejected her defence in a trial that lasted just half a day.

The Ho Chi Minh City Police newspaper, controlled by the city's police, said Huong had failed to prove the other woman was real.

The court ruled the offence was "extremely dangerous to the community" and found her guilty, and she now faces death by lethal injection.

Australian officials assisting woman and her family

Australia's Department of Foreign Affairs and Trade said it was providing consular assistance to Huong and her family.

"We are concerned that an Australian citizen has been sentenced to death in Vietnam," the department said in a statement.

"According to Vietnamese law, the accused can appeal the sentence so there is still some way to go before this legal process concludes.

"We will continue to provide consular assistance and support to the woman and her family."

Huong has 15 days to appeal against the death sentence.

The statement also stressed Australia's long-standing opposition to the death penalty.

Vietnam has some of the toughest drug laws in the world and the possession of even small amounts of heroin can result in capital punishment.

ABC/Reuters