Rebuilding the financial reputation of the United States will be Gary Locke's top priority when he arrives in Beijing on Friday as the US ambassador to China, experts said.

"Amid the concerns over the gloomy economic future of the US, it is Locke's responsibility to relieve the anxiety in China toward US debt after the downgrade of US government credit rating," said Zhou Qi, a researcher at the Chinese Academy of Social Sciences.

US stocks continued to be volatile on Wednesday, closing down more than 500 points. The market's rollercoaster ride started Monday after Standard & Poor's downgraded the US rating from AAA to AA+ on Friday.

China is by far the largest foreign holder of US debt, with holdings of $1.16 trillion in May, US Treasury Department data show.

The US government has recently lifted its debt ceiling in order to avoid a default, but Chinese officials and economists still expressed concern about the uncertainty in the US economy.

Locke has plenty of work to do as the new US ambassador to China, but boosting the credibility and stability of US debt and minimizing the side effects brought by the US' recent credit rating downgrade is certainly among the most important tasks, Zhou said.

Locke is expected to arrive in Beijing on Friday with his wife, Mona, and their children, Emily, Dylan, and Madeline.

His arrival, five days before US Vice-President Joe Biden's visit to China on Aug 17, will "excitedly open a new chapter for Sino-US relationship", the US embassy's official micro blog said.

Zhang Zhixin, a US expert from the China Institutes of Contemporary International Relations, said Locke will emphasize three topics in his role as ambassador.

"He will help US companies better their business in China and possibly take some measures to handle the intellectual-property-rights problem, which has been a long-existing pain for those doing business in China," he said.

Zhang said Locke will also look into the issues regarding regional security, such as the nuclear issue in the Democratic People's Republic of Korea.

And he will certainly engage in public diplomacy, promoting human rights and Western values, Zhang added.

The 61-year-old Locke was nominated by US President Barack Obama in March after Jon Huntsman stepped down to prepare to run in the 2012 presidential election as a Republican candidate.

Locke was sworn in earlier this month as the first Chinese-American to serve as ambassador to China. His nomination to the post was warmly received by China.

The central government believes his Chinese roots and close ties with the White House will bring Beijing and Washington closer. But tough challenges remain, such as issues over trade, security and human rights.

"President Obama clearly regards the Sino-US relationship as one of the most critical relationships for the US by nominating Gary Locke as the US ambassador to China," said Jin Canrong, of Renmin University of China, adding that Locke will be easily accepted by China because of his Chinese-American heritage.

Obama praised Locke as "one of our nation's most respected and admired public servants" and said no one is more qualified than him to replace Huntsman.

Before Obama appointed him as commerce secretary in 2009, Locke served as governor of Washington from 1997 to 2005. As governor, he doubled the state's exports to China.

Locke's grandfather came to the US over a century ago to work as a house servant for a family in the state of Washington in exchange for English lessons. His father was also born in China and moved to the country as a teenager.