Vietnamese authorities have seized marijuana worth $90 million in the country's biggest drugs haul, police said Thursday.

The 8 tons of marijuana was believed to be in transit to Canada via China, said Col. Nguyen Anh Tuan, director of the Ministry of Public Security's Anti-Drug Department.

He said the marijuana was seized earlier this week on two trucks heading for the border with China. It had arrived in the port of Hai Phong in late April on a ship from Pakistan and was ultimately destined for Canada.

The drugs had been mixed in with a shipment of blue jeans, he said. "This is the biggest drug shipment we have ever seized," Tuan said.

Four Chinese and an Indonesian have been arrested in connection with the smuggling and others were being sought, Tuan said. It's unclear when the five will be put on trial.

Vietnam has one of the world's toughest drug laws. Possessing, trading or trafficking 1.3 pounds of heroin or 44 pounds of opium is punishable by death or life in prison.

About 100 people are executed by firing squad in Vietnam each year.