Police in Quang Nam Province have seized a vehicle containing more than three tons of cyanide, a poisonous chemical used in gold mining.
Bui The Tien, an officer with the Quang Nam police force said they have arrested Cao Dinh Phuong, 28, and Le Thi Huong, 40, owner of the car that transported the deadly chemical compound.
Phuong was allegedly driving the vehicle when it was stopped by the authoritites.
The chemical was stored in 16 oil tanks, being transported from Hanoi to gold mines in Quang Nam, local news website VietNamNet reported.
Tien said he seized two mobile phones belonging to Phuong and Huong, the car and VND30 million (US$1,540) in cash pending further investigation.
Police estimate that the traffickers would have earned more than VND300 million if the transport proved successful.
This is the biggest cyanide trafficking case in Vietnam ever.
In May, police in Da Nang found two tons of cyanide on a bus bound for the neighboring Quang Nam.
Unofficial statistics provided by authorities indicate that illicit gold miners in the mountainous regions employ thousands of tons of cyanide every year.
The chemical is used in gold mining to separate the precious metal from other substances. The compound tends to severely pollute streams around the mines.