Yang Bay Tourist Park had held the animals in cages for years to amuse tourists, but was recently persuaded by animal right activists to hand them over to Animals Asia, a Hong Kong-based foundation that has rescued over 600 bears and cares for them at sanctuaries in China and Vietnam.

The animals will be taken to the Vietnam Bear Sanctuary in Tam Dao District in Vinh Phuc Province near Hanoi. The sanctuary spreads over 11 hectares (2.5 acres) and has an outdoor semi-natural enclosure of almost 30,000 square meters, which stimulates bears’ natural behaviors.

After being kept in isolation at the sanctuary for 45 days the animals will be transferred to the enclosure with some 200 other bears.

In a Facebook post, Animals Asia said it received information the four bears might have been abused in circuses before ending up at the park, given the scars on their bodies.

Vietnam is home to both the moon bear and the sun bear, listed as vulnerable species by the International Union for the Conservation of Nature. It estimates that Vietnam has 700 bears in captivity as people are allowed to keep them if they are registered with the authorities.

Most owners claim to keep bears because they "adore" and want to "conserve" them. But it has been found that bears are actually raised to extract their bile for sale. In China and Vietnam, as traditional medicine practitioners advertise, bear bile is a remedy that could be effective for a list of sickness, from hangovers to cancer.

The Forest Protection Department has said the number of bears in the wild in Vietnam has dropped to just a few hundred individuals.