Chinese authorities have announced plans to control video gaming as a response to rising levels of near-sightedness among children.
Regulators want to limit the number of new games, restrict playing time and develop an age-restriction system.
A report in 2015 found 500 million Chinese suffered visual impairment, nearly half the population over five.
China is the world's biggest gaming market and shares of local tech firms dropped sharply in response.
The Chinese ministry of education released the new policy plans on Thursday after President Xi Jinping earlier this week called for greater national attention on optical health.
The document blamed the high levels of myopia on a heavy study load, the spread of mobile phones and other electronic devices, and a lack of outdoor activities and exercise.
There is no consensus that gaming is causing myopia but studies have raised it as one possible cause.
There has been a massive rise in short-sightedness around the globe in recent decades, with East Asian countries having the highest rates.
Stocks of Chinese gaming companies plunged on Friday in response to the new policies.
Tencent Holdings' market value slumped $20bn (£15.37bn) amid fears of heightening regulatory risks for companies.
The firm is thought to account for 42% of the country's mobile gaming market.