BEIJING - Branches of the United States-registered non-government organizations (NGOs) in the Chinese mainland number about 1,000, according to a report released Friday by the China Charity & Donation Information Center.

These NGO branches mainly fall into categories of humanitarian aid, environment and animal protection and interests safeguarding for women and laborers, according to the report from the center under the Ministry of Civil Affairs.  

The American NGOs have injected nearly 20 billion yuan ($3.18 billion) of donations into China since 1978, when China started its reform and opening up, said the report.

The American NGOs recently have injected an average of $295 million into China every year.These funds mainly have gone into higher education colleges,  scientific research institutions and government organs, said the  report.

But the American NGOs' activities in China also posed potential risks and challenges, said the report, without detailing the problems.

The report also called on the American NGOs in China to improve their policies and institutional construction.

The center will continue to conduct analysis to foreign NGOs' branches in China so as to provide a reference to Chinese NGOs and policymakers, as well as provide a knowledge for the public about the foreign NGOs and a guidance for foreign NGOs operating in China, according to the report.