China will return giant pandas to Washington's National Zoo by the end of the year, US First Lady Jill Biden and officials said on Wednesday in a surprise announcement signalling a new era of panda diplomacy between the two superpowers.

"We are excited for children near and far to once again enjoy the giant pandas' adorable and joyful adventures at our @NationalZoo," the first lady posted on X.

Beijing will send a new pair called Bao Li and Qing Bao under a 10-year breeding and research agreement, the zoo said in a statement, hailing a "historic moment" that demonstrated the benefits of its partnership with Beijing.

"We're thrilled to announce the next chapter of our breeding and conservation partnership begins by welcoming two new bears, including a descendent of our beloved panda family, to Washington, DC," said Brandie Smith of the Smithsonian's National Zoo and Conservation Biology Institute.

"This historic moment is proof positive our collaboration with Chinese colleagues has made an irrefutable impact."

Amid tensions between Beijing and Washington, only a handful of the iconic black and white bears remain in the US, with three having left the national zoo in Washington six months ago.

But President Xi Jinping said after meeting President Joe Biden at a summit in California last November that China could send new pandas as "envoys of friendship between the Chinese and American people."

The White House said it would be happy to have more bamboo-chewing bears.

China has been using so-called "panda diplomacy" since 1972, when the first animals were sent to the United States as a gift, following then-president Richard Nixon's historic visit.

Strained relations between the rival superpowers in recent years have led Beijing to call some of the pandas back home.

All three giant pandas at the Smithsonian National Zoo in Washington – Mei Xiang and Tian Tian, who arrived in 2000, and their three-year-old cub Xiao Qi Ji ("Little Miracle" in English) – flew back on a cargo plane to China in November last year.

The currently last remaining pandas in the US, at a zoo in the southern city of Atlanta, are due to return to China later this year, although China announced plans in February to send a new pair of giant pandas to the San Diego Zoo. (AFP)