Market insiders said the two sides have yet to sit and agree a new cooperation channel.

But, experts also cited capital market reforms in Hong Kong and the mainland as a big reason why US-listed Chinese companies are returning to home exchanges.

To make public offerings easier for new-economy businesses, the Hong Kong bourse had allowed companies with dual-class shares, a special equity structure preferred by many technology firms, to get listed in 2018. This paved the way for secondary listings from Alibaba and JD.

Meanwhile, Chinese authorities also stepped up efforts to enable technology firms to return home for financing. Landmark progress last year in the form of the debut of Shanghai's STAR Market, which is dubbed the sci-tech innovation board, is a shining example of capital market reforms.

President Xi Jinping announced in November 2018 that China would launch the STAR Market and pilot the registration-based system for IPOs to give full play to market forces and to ensure more inclusiveness, in order to benefit technology firms.

Semiconductor Manufacturing International Corp, a Chinese chipmaker, has since re-listed on the STAR Market in July, after delisting from New York last year.

The registration-based reform has been replicated on Shenzhen's ChiNext board, while the country eased the requirements for secondary listings on mainland bourses in April.

"Recent reforms have made both Hong Kong and Shanghai more friendly to fast-growing technology companies," said Stephanie Tang, China head of private equity with Hogan Lovells, a global law firm.

"High-quality Chinese companies now have multiple alternatives (to US exchanges) available to raise capital and carefully weigh each listing venue's trade-offs."

As the US-listed Chinese firms return home to raise fresh funds, Hong Kong and mainland exchanges sense a strategic opportunity to improve the quality of companies listed on them, making it easier for local investors to invest in the country's best growth companies, experts said.

"The return of overseas listed Chinese stocks to home exchanges means that Chinese investors have the opportunity to invest directly in those high-quality targets, which will cement the attractiveness of renminbi-denominated assets," said Cheng Shi, chief economist at corporate financing platform ICBC International.