Zookeepers in Beijing worked frantically to keep their residents warm as temperatures in the capital plummeted over the weekend.

But with 5,000 animals - 500 species from five continents - they had their work cut out for them, according to Beijing News.

For instance, cold can damage hippos' skin, officials say, so most of the hippos have been spending time in hot spring water.

Over in the reptile enclosures, heaters have been going full-blast to keep the Burmese python alive in temperatures of around 30 C.

In the turtle tanks, a wireless temperature monitor has been used to keep the room warm, with automatic alerts telling keepers when the temperature drops below a certain level.

Recently, the zoo agreed to set up another 20 shelters to help stray cats keep warm, on top of the 25 it already had.

The shelters and litters were provided by volunteers from the Capital Animal Welfare Association. Volunteers were worried after many strays died from the cold during snowfalls in Beijing on Dec 12.

In Shanghai, animals have also been given similar treatment against the cold.

"We have been taking particular care of the animals from tropical areas," said Xu Zhengqiang, a staff member of the animal protection office at Shanghai Zoo, on Sunday.

Its two-toed sloth, a newly arrived guest from South America, has been enjoying 24-hour monitoring in a specially air-conditioned room, and has only been allowed outside on occasional warm sunny afternoons.

"For different types of animals, we have different approaches to keep them comfortable and healthy," added Xu.

Most of the animals are fed on a "high-energy diet" so their body can store enough fat to fight against the cold, he said.

To save energy and better protect the animals, the zoo has also changed some of its heating systems from oil to natural gas this year.

"So far all of our animals have remained very healthy, and we have not had any with colds or fever."