Two bears frolic in the playground at the Vietnam Bear Rescue Center in Chat Dau Valley, part of the Tam Dao National Park, an hour and a half to the north of Hanoi.

The center spans 12 hectares and is the largest of its kind in Southeast Asia. It has around 200 moon bears and sun bears, many of which used to be held captive for bile harvesting.

A bear is taken into a surgery room inside the center.

Upon arrival at the center, the animals are quarantined and carefully monitored for 45 days. Health checks, including x-rays and examination of teeth, mouth, feet, and claws, are done once every two years.

Staff at the center prepare foods for the bears. Fruits, carrots, sweet potatoes and milk are on their menu.

The center has around 100 workers and experts, including foreigners, to take care of the bears.

Hoang Van Chien, a manager at the center, prepares food for the bears.

Chien said the bears are fed three times a day, twice outside and once inside their enclosures, before they go to sleep.

A worker trims grass in a field which serves as the bears' playground. Workers often hide food items in bushes or on trees for the bears to find.

A worker sets up electric wires around an enclosure. All enclosures are closed and electrified after 8 p.m.

Chien said: "Five amps of electricity flows through the fences of the semi-wild enclosure. The bears step back if they touch an electrified fence, and after doing that a few times they learn not to go near the fences."

A bell is rung to signal to the bears to come out to the playground to play and eat.

A group of bears come out of their enclosures and into the playground.

Each enclosure is 2,000-3,000 square meters large and houses 20 bears. If a bear cannot get along with the rest of the group, it is moved to a different enclosure.

Two sun bears at the center. They are often kept as pets, but sun bears raised in captivity are not capable of foraging for food. As there is no guarantee the bears can survive on their own outside, most of them live at the center for life.

Aerial view of the Vietnam Bear Rescue Center.

Around 600 bears are still held captive across Vietnam. Both the moon bear and sun bear are listed as vulnerable species by the International Union for the Conservation of Nature.