A large amount of personal information about Chinese train passengers has been leaked, Beijing police said on Tuesday. 

The Beijing Public Security Bureau's cyber security squad discovered on Thursday that data about more than 4.7 million passengers had been stolen and sold by an internet user identified as "deepscorpions". 

China's national rail operator said on its microblog later that day that no user information had leaked from its widely used 12306 China Railway rail ticket booking site and denied online rumors it had been hacked. 

After investigating, police officers tracked down a 25-year-old suspect surnamed Chen and detained him on Saturday at a tech company in the capital's Xicheng district. 

Chen confessed to illegally purchasing 600,000 passengers' online registration information from a tech company, and said he had not hacked the 12306 China Railway website. He also admitted obtaining personal information of over 4.1 million passengers through a third-party online booking platform.