Three Siberian tigers are seriously ill at a northeast China zoo where 13 others had died, experts said Monday.

Comprehensive examinations of the 30 remaining tigers in the Shenyang Forest Wildlife Zoo Monday showed three had problems, said Zhao Yujun, one of the zoologists conducting the examinations.

A Siberian tiger is seen at the Shenyang Forest Wildlife Zoo in Liaoning province on Saturday.[Xinhua]

They were shedding fur, had lost their appetites and were listless, experts said, blaming it on the humid and sunless accommodation.

Nutrition injections had been given to save the tigers, said Zhao.

Food supplies had been ensured and other tigers at the zoo were each eating at least 2.5 kg of beef and two hens a day.

More than 20 heating and lighting facilities had been installed since Sunday. Disinfection and ventilation measures had been adopted and food and water drinking conditions improved.

The government of Shenyang has allocated 7 million yuan (US$1.03 million) to fund the zoo, which is mainly privately owned with the Shenyang Municipal Government having a 15-percent stake.

An investigation team is probing the causes of the deaths of the tigers and disposal of tiger parts, the previous use of government funds, and the dispute between employees and zoo management and the operation of the zoo.

The news of the dead tigers was broken by zoo workers who stopped work last Wednesday to demand their salaries, which were 18 months in arrears.

Thirteen Siberian tigers died over three months at the zoo: 11 of them from malnutrition and two were shot after mauling a worker in November 2009.

Zoo workers said many other animals had died, including rare species.

The number of animals in the zoo has dropped by half in a decade, from 1,020 animals of 61 species in 2000 to 518 of 49 species in 2010.