Thousands of rare forest turtles have been rescued from horrifying conditions of captivity in the Philippines, saving the critically endangered animals from possible extinction, wildlife experts said Wednesday.

More than 4,000 live freshwater turtles and 90 dead ones were found in a pond inside a remote warehouse on the western island of Palawan four weeks ago in one of the country's biggest wildlife rescues, they said.

They included 3,831 Palawan forest turtles, a critically endangered species found only on the north of the large island, as well as 160 Asian leaf turtles and 25 Southeast Asian box turtles.

"The turtles were in terrible conditions," said Sabine Schoppe, director of the Philippine Freshwater Turtle Conservation Programme.

The reptiles had apparently been stored without food and water for up to six months, and veterinarians worked round the clock to save the animals, she said in a statement.

The turtles were apparently destined for pet and food markets in Hong Kong and China, the statement said.

"This number equalled the estimated remaining population of Palawan forest turtle in the wild, hence bringing the species to the brink of extinction," it added.

Many of the rescued turtles suffered from a variety of ailments and injuries, and some 360 others have since died.

About 230 are still being treated, while the rest were released back into the wild, Schoppe said.

Wildlife officials raided the warehouse on June 17 in the town of Bataraza, near the southern end of Palawan about 750 kilometres (miles) southwest of Manila.

The warehouse caretaker was questioned by police but not detained, said Jennifer Lyn Yap, member of the regulation and enforcement division of the Palawan Council for Sustainable Development, a government body tasked with protecting the island's rich wildlife.

The owner remains at large, she added.

The turtles were transferred by truck to a rescue centre for critically endangered Philippine crocodiles in the provincial capital Puerto Princesa, the only location on the island capable of housing such large numbers of rescued animals.

Trapping or trading in Palawan forest turtles is punishable by jail terms and huge fines.

Wildlife authorities suspect northern Palawan poachers had sold the turtles to a trader who transported them to the other end of the island.

"Our assumption is they would have ended in the Chinese markets, where they are sought after as food or pets," Yap said.

The rescued leaf turtles are considered "near threatened" by the Swiss-based International Union for the Conservation of Nature.

Southeast Asian box turtles are deemed "vulnerable" by the same organisation.