LHASA, July 3 (Xinhua) -- The survey of old documents at Norbulingka, an ancient palace, has covered 745 ancient books since last September, said researchers in southwest China's Tibet Autonomous Region.

The palace's management office and the regional ancient book protection center jointly launched the survey in the palace last September.

Some ancient books at Norbulingka were found to be moth-eaten and have paging disorder, which the researchers will record in detail on the computer and the notebook for the survey, according to Nyishar, director of the ancient books department of the region's library.

"The departments that conduct the survey of the ancient books at Norbulingka are clear about their roles and responsibilities, which avoids secondary damage on the old documents resulted by repeated surveys in the future and provides other units with important reference of such surveys," said Nyishar.

Built in the mid-18th century, the palace was added to the UNESCO World Heritage List in 2001 as part of the historic ensemble of the Potala Palace.

Tibet is home to a massive collection of ancient books, and the region has completed a survey of more than 13,700 ancient books, accounting for over 65 percent of the region's total.