"We are seeing tremendous growth in this area - the Hong Kong, Shenzhen, Guangdong and Macao connection," said Joseph. "When you put together that cluster of cities, there's huge economic growth there — the tech companies, biotech companies, et cetera, are exploding with growth."

By building a bridge of financial and legal services and expertise in Hong Kong, the ability to make business grow and connect the Pearl River Delta to international business is very large, she said.

"We want to connect Chinese mainland companies that are growing very fast in the Pearl River Delta with Western companies that are also looking to do business," she explained. "It might be China firms that are looking to export or even manufacture in the US or build business partnerships with the US, or it might be Western companies looking to connect to the Pearl River Delta."

Beyond the Pearl River Delta, the US companies also are involved in the Belt and Road Initiative. The US engineering firm Aecom has been involved in a Belt and Road project to improve infrastructure and connectivity in the region.

"A lot of US companies are quite interested in getting involved in the initiative," said Joseph.

Next month a Belt and Road summit will be held in Beijing and Hong Kong will host another summit in September.

"We will be partnering at these summits and quite active to find out where we can be involved and fit in," she said.

AmCham HK also leads missions to Chinese cities, like Guangzhou, Beijing and Shanghai, every year.

"We are constantly interacting with Chinese mainland companies and government officials," said Robert T. Grieves, chairman of Hamilton Advisors Limited, a Hong Kong-based public relations consultancy.

He said the personal exchanges are great for people to find out what's really going on in the Chinese mainland.

The recent delegation to the Chinese mainland was very positive, said Agnes Tsang, director of government relations and public affairs with AmCham HK.

"The senior government officials the delegation met with were very open to Hong Kong cooperating with other cities in the Pearl River Delta. They would like to see these things happening as well," said Tsang.