BEIJING — Only 22 minutes after opening Monday morning, 2.15 billion yuan (around $320 million) of bonds had been purchased by overseas investors rushing to increase presence on the world's third largest bond market under the Bond Connect between the Chinese mainland and Hong Kong.

It was only a glimpse of brisk trading on the first day for the over-67-trillion-yuan market, which is still growing rapidly and opening wider across the globe.

HSBC Holdings was among the first traders. Helen Wong, HSBC Greater China chief executive, lauded the new scheme, saying it "will attract more overseas funds, creating a more diversified base and further enhancing the market's size and depth."

The Chinese authorities approved the bond link in mid-May, allowing investors from both sides to trade bonds on each other's interbank markets. Northbound trade started Monday, without caps on investment volume.

With the launch, which came after two similar stock connect programs initiated in 2014 and 2016, respectively, China has secured another solid step forward in its progressive but persevering drive to internationalize its financial sector and currency.

Addressing the opening ceremony, Pan Gongsheng, deputy governor of the People's Bank of China, said connectivity and integration of financial markets on both sides would be further improved, expanding the market size of Hong Kong and building easier investment channels to the mainland.

China's bond market boomed during the past decade but access for overseas investors is still limited, which has been accentuated as a more global yuan has stimulated demand for yuan-denominated assets.

So far, a total of 473 overseas investors hold 800 billion yuan of outstanding investment in the interbank bond market under several schemes including QFII and RQFII. Analysts believe the less than 2 percent foreign holding in the market provides ample room for much stronger improvements in the future.

Although an immediate, enormous boost will be unlikely, the bond connect will become a surefire driving force for the country's financial opening up.

The Beijing-based investment bank China International Capital Corporation (CICC) said in a research note that the initial inflows might be modest but it "signifies another step forward in opening up China's capital market and allowing mutual capital-market access between China and the rest of the world."

"It is a milestone in the internationalization of the RMB because it will greatly enlarge the pool of investable assets denominated in RMB as global investors will be able to hold and trade more RMB-denominated assets," said Ivan Chung, associate managing director at Moody's.

CCB International managing director Cui Li estimated that the Chinese bond market would see up to $100 billion of annual capital inflows during the next five years and combined foreign bond holding would account for 4 to 5 percent of the country's GDP.

Encouraged by the scenario, China Development Bank, one of the country's three policy banks, has said it will issue fixed rate financial bonds worth no more than 20 billion yuan under the new bond link for global investors on Tuesday, the largest such issuance. Agricultural Development Bank of China also announced a similar plan.

The bond link will also help the increasingly open Chinese market to gain more global recognition.

Citibank's index unit announced two new bond indices on China and the inclusion of Chinese treasuries in its series of government bond indices earlier this year.

"We expect more international bond indices will include or increase allocations in Chinese onshore bonds one year after the implementation of Bond Connect," Chung said.

Hong Kong's role underpinned

The Bond Connect came on the heels of the 20th anniversary of Hong Kong's return to the motherland on July 1.

Pan said the program represented "the efforts from the central government to reinforce and improve Hong Kong's role as an international financial hub and ...the resolve to support Hong Kong's long-term prosperity, stability and development."

The past two decades witnessed the ascent of Hong Kong's global competitiveness, supported by a sound business environment, solid infrastructure and a complementary mainland market.

Norman Chan, chief executive of the Hong Kong Monetary Authority, has said the region would continue to "be a gateway for overseas investors to enter the mainland bond market ... as well as an intermediary for capital flows between the mainland and international markets."