China has started selling naming rights for its bullet trains to commercial sponsors, state media reported Wednesday, as it increasingly commercialises its state-controlled railway sector.

Passengers on a train in southern China recently found it had been named for "China Unicom", one of the country's three telecom service providers, the Shanghai-based Oriental Morning Post said.

The Bank of China, one of the country's "Big Four" banks, and a food company, Luziyao -- whose products include nuts and pickled fish -- had also named trains after themselves, the newspaper said.

A city outside Beijing extolled its natural beauty by naming a train "Grand Rivers and Mountains Zhangjiakou", it said.

China has the world's largest high-speed rail network, but the sector has been rocked by scandals and corruption allegations, including a 2011 crash which killed at least 40 people and sparked an investigation which found evidence of bribery.

The government in March last year merged the railway ministry into another state agency and turned over its commercial functions to a new company, the China Railway Corporation.

A one-year sponsorship of a bullet train could cost 12 million yuan ($2 million), the Oriental Morning Post said, citing unnamed sources.

The move was driven by the fact that train operators were now accountable for their own profits and losses, sources told the Shanghai paper.

Social media users have leaped on the marketing possibilities.

One posting on the country's Twitter-like Sina Weibo suggested a condom maker as a potential client: "Attention passengers: The Durex High-Speed Train is now reaching the station. Durex wishes you a pleasant journey."