Tran Xuan Hiep, 30, and Nguyen Duy Phuong, 33, are under investigation for "trading human body parts," an offense punishable with life imprisonment.

Investigators said the two men, both Hanoi residents, had once sold their own kidneys and thus having experiences in the process and required procedures for illegal kidney trade.

The two relied on social media to source kidney donors and scouted hospitals to find patients in dire need of the organ.

They purchased kidneys priced at VND230 million ($10,000) each, resold for VND1.1 billion a piece.

Kidney donors were housed and looked after in rented premises in Hanoi while awaiting their operation.

Any successful deal brought them VND200-300 million.

In early February, the two traffickers agreed to sell kidneys to two patients at a hospital in Hanoi when apprehended by police.

An investigation subsequently uncovered four more donors looking to profit from trading their organs.

Hiep and Phuong told police they had already conducted several successful kidney trades.

More than five million people have chronic kidney disease in Vietnam, and 100,000 have to receive dialysis daily, official data shows.

Social insurance only funds the cost of dialysis, so those who need a transplant have to pay for it.

Then, those with kidney failure have to register to wait in line for a legal kidney, which normally takes several months or even more due to a serious donor shortage. This has prompted many kidney patients to gradually lose hope and turn to the black market. In many cases, donors and receivers have no information on each other.

In Vietnam, where organ donation is considered a taboo as many believe one should die wholly prepared for the afterlife, black market kidney transactions like Binh and Tien's are not rare.

According to police, kidney traffickers usually conduct 30-50 deals per year.