The National Press and Publication Administration told state-run news agency Xinhua that game-playing would be only allowed between 8pm to 9pm.
It also instructed gaming companies to prevent children playing outside these times.
Earlier this month a state media outlet branded online games "spiritual opium".
Inspections of online gaming companies will also increase, to check that the time limits are being enforced the regulator said.
Earlier rules had limited children's online game-playing to 90 minutes per day, rising to three hours on holidays.
The move reflects a long running concern about the impact of excessive gaming on the young.
A month prior to the latest restrictions, an article published by the state-run Economic Information Daily claimed many teenagers had become addicted to online gaming and it was having a negative impact on them.
The article prompted significant falls in the value of shares in some of China's biggest online gaming firms.
In July, Chinese gaming giant Tencent announced it was rolling out facial recognition to stop children playing between 22:00 and 08:00.
The move followed fears that children were using adult ID's to circumvent rules.
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