Almost a third of the Great Wall of China has disappeared, due partly to locals stealing bricks to sell to tourists as souvenirs.
Chinese state media said some of the bricks from the Wall had also been used to build homes.
Natural decay has also been accelerated by harsh weather conditions, according to data from the State Administration of Cultural Heritage.
The organisation estimates about 2,000 kilometres – around 30% of the Wall – has been lost.
"Even though some of the walls are built of bricks and stones, they cannot withstand the perennial exposure to wind and rain," said Dong Yaohui, vice president of the Great Wall of China Society.
"Many towers are becoming increasingly shaky and may collapse in a single rain storm in summer."
Dong has urged authorities to make a full inspection and start comprehensive repair work where needed.
There are well established laws against stealing bricks but enforcement is lax, cultural relics protection officer Jia Hailin told the Beijing Times.
"There is no specific organisation to enforce the rules. Damage could only be reported to higher authorities and it is hard to solve when it happened on the border of two provinces."
The report also said there are an increasing number of tourists visiting less developed sections of the wall, putting more strain on its already fragile condition.
