Between 2017 and May 2018 Trieu Ky Voong, 50, Pham Xuan Lan, 38, Song A Sang, 36, and Lieu Van Cay, 45, transported heroin from Son La Province at the Laos border, via Hanoi and Lang Son Province at China border, to China, media reports said.

Lan was caught with 6.6 kg on a truck going from Son La to Lang Son on May 16 last year. Investigations led to the arrest of the other three.

Voong was the mastermind who worked with Sang to traffic the drugs, while Lan was the mule carrying them from Son La to Lang Son and Cay delivered them to their final destinations.

To hoodwink authorities, Voong used the money earned from drug trafficking to open restaurants and hotels in Lang Son.

The court also slapped fines of VND3.1 billion ($133,450) on Voong, VND170 million ($7,300) on Lan, VND150 million ($6,450) on Sang and VND100 million ($4,300) on Cay.

Vietnam is a key trafficking hub for drugs from the "Golden Triangle," a lawless wedge of land straddling China, Laos, Thailand, and Myanmar that is the world's second largest producer of drugs.

Drug busts and convictions have been increasing in Vietnam despite the country having very tough laws.

Those convicted of possessing or smuggling more than 600 grams of heroin or more than 2.5 kilograms of methamphetamine face the death penalty.

The production or sale of 100 grams of heroin or 300 grams of other illegal narcotics is also punishable by death.