More than 40 sites have been restored by local governments after Tang posted pictures. And he sometimes revisits places to see the restoration progress.

A major problem is that many historical buildings are not officially recognized as cultural relics. Some people or developers have dismantled, relocated or taken away parts of buildings to sell, without official approval.

"I hope our constant exposure of these crimes prompts local governments to intensify preservation efforts," says Tang.

Commenting on his work, a web user with the screen name "Jiandan" says: "I am touched by his passion. I hope more people join in to take care of the neglected historical sites."

Tang calls himself "Aiguta" online, which means "love pagoda".

His love for pagodas goes back 30 years to his high school days, when he read a book on Chinese pagodas.

But now, his passion covers more buildings.

Tang does not mind spending his money and time to save and study relics. "It's worth every moment," he says.

ASSOCIATED PRESS