Apple removed 2,500 games from its App Store in China in the first week of July, reports market researcher Sensor Tower. That is four times as many as were removed from the App Store a month earlier. The increase is likely due to app builders failing to report in time whether their game has been approved by the government.

The removed games include titles from Zynga (known from FarmVille and Words with Friends ) and Supercell (known from Clash of Clans and Hay Day ).

Apple gave game builders in China until the end of June the opportunity to provide a license number to the company. It is a number that makes it clear that the Chinese government agrees that small purchases can be made in the game. In app stores on Android smartphones, apps had to make their license known for some time.

Sensor Tower has not been able to determine the cause of removal individually for each game, but calls the peak remarkable. The games may return to the App Store in the future.

China has tightened controls in the video game market. Companies must go through an extensive process to obtain approval to operate in the Chinese market.