Two more U.S.-listed China companies have announced plans to launch secondary listings in Hong Kong. The companies are the latest to announce listings closer to home as tensions between China and the U.S. continue to escalate.

Several big China companies listed on U.S. exchanges have already launched secondary listings in China - likely hedging against risks over the growing political tensions. This week, e-commerce company Baozun and pharmaceutical company Zai Lab Limited, both listed on the New York Stock Exchange, have announced plans to list in Hong Kong.

The two companies, both based in Beijing, announced they would be selling additional shares in Hong Kong in September. The planned share sales are expected to add to the growing number of initial public offerings in China's financial hub in September - which have already exceeded a combined value of around $4 billion. Accounting for the two planned listings, September is looking to become the busiest month for the Hong Kong Stock Exchange this year.

China e-commerce company Baozun, which is partly backed by Alibaba Group Holding Ltd., plans to start its share sale Friday. The company will offer 4 million shares to Hong Kong market participants and 40 million for international investors. Baozun wants to raise $500 million.

Meanwhile, pharmaceutical manufacturer Zai Lab plans to sell 771,000 shares in Hong Kong and 9.79 million shares to international investors. The company seeks $832 million.

The steady march of U.S.-listed China companies choosing to launch secondary listings in China began with Alibaba's $13 billion listing in November. Alibaba was followed by other U.S.-listed China companies including NetEase,, and Yum China Holdings.

NetEase and raised a combined $7.5 billion in June. Several other China companies followed over the following months. Earlier this week China warehousing company ZTO Express raised $1.6 billion. Shanghai-based Hauzhu Group raised around $782 million in an initial public offering.