The trade sanctions that the United States plans to impose on Hong Kong over a proposed national security law for the city are a "mistake", and the US will emerge "the biggest loser" from the move, expatriates said.

"The sanctions are a way for the US to kind of get to China, but it would just hurt the US in the long term more than anybody," said Cyrus Janssen, a US international business adviser who used to live in Hong Kong.

US President Donald Trump instructed his administration on May 29 to revoke Hong Kong's "preferential" treatment as a separate customs and travel territory from the Chinese mainland. The move came after China's top legislature decided to enact a national security law for the special administrative region to close a long-standing legal loophole in the city.

Janssen said the sanctions on Hong Kong will heighten the US' dire unemployment rate, which has spiked this year as a result of the COVID-19 pandemic.

According to the US Department of Commerce, the country's exports of goods and services to Hong Kong supported an estimated 188,000 jobs in the US in 2015.

Trade between the US and Hong Kong "influences 188,000 jobs in the US, so this is going to really affect the US ourselves by sanctioning," Janssen said.

Meanwhile, Janssen, who lived in Hong Kong from 2014 to 2017, said he believes the international financial and business hub's glamour won't fade because of the US sanctions, as the city has good trade links with many countries and regions around the world, and other places will continue their mutually beneficial relationships with Hong Kong.

"I think it's going to remain the financial hub and a very powerful city in Asia," he said.

Angelo Giuliano, a Swiss financial consultant who has lived in Hong Kong for three years, echoed Janssen's sentiments, saying that Washington's sanctions against Hong Kong are a big mistake, as the trade balance between the two places has always favored the US.

From 2009 to 2018, the accumulative merchandise trade surplus that the US had from Hong Kong reached a hefty US$297 billion.

Giuliano said he still has faith in Hong Kong's markets. "Many investors fled Hong Kong before 1997 and went back to the city a few years later," he said.

He said Beijing has kept its word on the protection of capital and investments in Hong Kong, and will continue to do so under the proposed national security law.

In addition, the US expat said it's very unusual for Hong Kong not to have enacted a law related to safeguarding national security, as most countries and regions around the world have such a law in place.

Janssen said he loves the city where he and his wife were married and where their daughter was born. But the couple decided to move from Hong Kong to Canada in 2017 as they wanted to raise their three children in a society free of political turmoil.

Janssen said he felt terrible when he learned that a large number of Hong Kong young people, including juveniles as young as 11, broke the law and were arrested during last year's social unrest.

He said he believes the proposed national security law will bring hope and prosperity back to Hong Kong.

Janssen disagreed with claims that Hong Kong no longer enjoys a high degree of autonomy — accusations that surfaced last month after the National People's Congress, the nation's top legislature, announced it would put forward a draft decision on national security legislation for the city.

"It's in China's best interest to keep Hong Kong autonomous. The central government wants to continue that, as the country benefits tremendously form the city's autonomous status," he said.

Brighter days lie ahead for Hong Kong after the new law is enacted, Janssen said.