Vietnamese cops have seized $3m (£2.2m) worth of heroin smuggled inside packets of tea, in the communist state's largest ever drugs haul.

Police caught Vu Chu Senh, 44, and his wife Mua Thi Do, 39, carrying 170kg of heroin on their motorbikes in the mountainous northern province of Dien Bien on Tuesday (2 January), according to state-run police newspaper Cong An Nhan Dan.

The drugs had come from from Laos packed into 489 packets of Thai-branded tea.

"The operation was very successful, capturing an especially large amount of heroin," said the deputy head of Dien Bien provincial police Le Cong Binh.

Police say the heroin was being transported through Vietnam to a third country, but did not give further details.

Vietnam borders China – the largest drug market in Asia – but also has a long coastline that leads to other large drug markets such as the Philippines and Australia.

Vietnam is a key part of the Golden Triangle drugs hotbed, which covers Laos, Thailand and Myanmar.

The area is the world's second largest drug producing region and is awash with methamphetamine, opium and heroin – the refined product of poppies. The world's biggest drug region is Asia's Golden Crescent area, which covers Afghanistan, Iran, and Pakistan.

Vietnam has some of the world's toughest anti-drug laws, with punishments ranging from stiff jail terms to capital punishment.

Anyone found guilty of possessing more than 600g of heroin, or more than 20kg of opium, in the country can face the death penalty.