A court in southern Vietnam has sentenced an Australian citizen to death for heroin trafficking.

Tuoi Tre newspaper said Nguyen Thi Huong, 73, was convicted of trafficking 3.5 pounds of heroin by a court in Ho Chi Minh City in a trial that lasted half a day on Wednesday.

Huong, who was originally from Vietnam, was arrested in December 2014 when checking in for a flight to Australia after the heroin was found hidden in 36 bars of soap in her luggage.

The court rejected Huong's statement that a woman gave her the soap bars and that she did not know that they contained the heroin.

Vietnam has some of the world's toughest drug laws where trafficking even small amounts of heroin is punishable by death.