Policy researchers voiced optimism on Sino-US bilateral ties after the White House announced its choice for the next top envoy to China, and they urged the United States to stop worsening one of the world's most critical bilateral relationships.

In a bid to end one of the longest vacancies of the post since the diplomatic ties were established in 1979, US President Joe Biden announced on Friday that Nicholas Burns, a career diplomat who has served presidents of both major political parties, is his pick for ambassador to China.

The announcement ended months of speculation on who would take up the position after Terry Branstad left Beijing in October. The nomination, once made official, will await expected Senate confirmation.

Policy analysts from both countries have seen the start of the long vacancy as a sign of the grave damage brought by the decoupling strategy sought by the administration of former president Donald Trump.

Since Biden was sworn in, the two countries have seen their ties further strained over a long list of topics, including the Taiwan question, human rights and COVID-19 origin tracing.

Diao Daming, an associate professor of US studies at the School of International Studies of Renmin University of China, said, "Although it is unlikely the Biden administration will change its China strategy after Burns assumes his new role, his coming to the position will at least help boost the level and quality of bilateral communication and contacts.

"This could be viewed as a positive signal with limited effect on China-US relations," Diao added.

The nomination came a little more than three weeks after China posted its new ambassador to Washington, Qin Gang, on July 28.

Both sides have shown goodwill at working levels at Qin's first meeting as top Chinese envoy with US Deputy Secretary of State Wendy Sherman earlier this month in Washington.

"China and the US are two major countries with interwoven interests", and "both countries stand to gain from cooperation and lose from confrontation", Qin said on Thursday while meeting with Stephen Orlins, president of the National Committee on United States-China Relations.

Burns "will act as a critical bridge between the world's two largest economies", according to Bloomberg, which added that "the Biden administration indicated it plans to maintain former President Donald Trump's tough stance toward Beijing" while seeking cooperation on issues such as climate change.

Wang Dong, a professor and executive director of the Institute for Global Cooperation and Understanding at Peking University, said the Biden administration "has been reluctant to break away from the previous administration's approach of repression and encirclement against China".

"It seeks comprehensive competition as well as selective collaboration with China, which has become a bipartisan consensus and a key element of Washington's China policy," Wang said.

In recent months, US diplomats have variously defined Washington's ties with Beijing as "competitive", "collaborative" and "adversarial".

The definitions aim to "leverage competition to contain China's growth and secure the US' global leadership and hegemony", Wang said.

Wang noted the hawkish atmosphere toward China in the US as well as the Biden administration's need to advance a domestic political agenda ahead of midterm elections next year.

"The US leadership is expected to take a balance between its short-term calculation for political interests and a long-term strategic perspective (on ties with China)," Wang added.

While Branstad, a former governor of the state of Iowa, had little diplomatic experience before becoming ambassador, Burns has deep political ties and diplomatic experience.

He served as US ambassador to the North Atlantic Treaty Organization from 2001 to 2005 and as US ambassador to Greece from 1997 to 2001, and was a spokesman for the State Department from 1995 to 1997.

Diao, the Renmin University of China scholar, said Burns has a certain degree of global perspective, has been engaged in the affairs of a number of regions, and worked for the administrations of former presidents Bill Clinton and George W. Bush.

"The Biden administration chose him partly to underline the bipartisan consensus on China policies," Diao said.

Also on Friday, Biden announced his intention to nominate Rahm Emanuel as ambassador to Japan. Emanuel is a former mayor of Chicago and was chief of staff for former president Barack Obama.

Su Xiaohui, deputy director of the Department of American Studies at the China Institute of International Studies, noted that it has taken months for the Biden administration to officially nominate people for a slew of key diplomatic posts.

"This reflects a series of challenges at home and abroad, and Washington needs some time to sort out its top priorities among various critical tasks," Su said, adding that "the Biden administration has been prudent in deliberating its next top envoy to China".

Burns is a trustworthy candidate for Washington, as he has been a senior career diplomat who once served as undersecretary of state, she said.

"Although he could not be defined as a China hand, he does have a background in researching the US-China relationship and he is familiar with the ties," Su said.

Biden has chosen Burns "in an effort to advance the future agenda regarding the Indo-Pacific strategy, as Burns aligns with him on a range of topics such as US values, ideology and the concern about the US military advantage in the region", she added.

In addition, Burns has said the two countries could work together on topics such as climate change and the COVID-19 response, Su said.

"It remains to be seen if he can tackle China-US ties in a more balanced and cool-headed approach as US ambassador, instead of simply implementing the commands from Washington," she added.

The nomination reflects that "the state of US-China relations now is unprecedented" and that Washington believes its relations with China "require a seasoned diplomat to deal with them", Chas W. Freeman, US assistant secretary of defense in 1993 and 1994 and a veteran China expert, said in a written interview.

Freeman said US Senator Ted Cruz of Texas is holding up every nominee for a foreign policy job to dramatize his opposition to the Nord Stream 2 natural gas pipeline, the flagship energy project between Russia and Germany.

"I would be surprised if ambassador Burns did not confront similar obstruction," Freeman said when asked about potential obstacles to Burns' nomination in the Senate.