China will restrict the number of video games and take steps to curb playing time by minors to address growing rates of childhood visual impairment as the government steps up its crackdown on the world's biggest online gaming market.

A statement posted on the Education Ministry website late on Thursday justified the new curbs as a way to counter worsening near-sightedness among minors, after President Xi Jinping earlier this week called for greater national attention on optical health.

But the move adds to perceptions that there is a broader campaign to rein in China's fast-growing video game sub-culture after authorities already made clear their concerns over gaming addiction and the violent content of many shoot-em-up titles.

The education ministry statement, also endorsed by seven other ministries, said they will "implement regulations and controls" on the number of games that can be played online, limit new releases, explore an age-restriction system for games, and take steps to reduce playing time by minors.

No specifics or timeframe were given.

Shares in internet giant Tencent, China's games leader, dropped by more than five percent in Hong Kong while Perfect World Co, a game developer formerly listed on the US NASDAQ exchange, fell as much as nine percent in Shenzhen.