Bao Bao Panda US china
Giant panda cub Bao Bao has become a diplomatic envoy for the US and China (Reuters)

A diplomatic freeze in relations between the US and China over territorial disputes in the East China Sea has been broken by an unlikely envoy - a baby panda.

The two superpowers were brought closer together to celebrate the first 100 days of a giant panda cub at the Smithsonian's National Zoo in Washington in what Michelle Obama described as a session of "Panda diplomacy".

The US first lady and her Chinese counterpart, Peng Liyuan, gave their blessing to the panda which was given the name of Bao Bao, Chinese for "treasure" or "precious", on its 100-day milestone.

The naming ceremony was attended by hundreds of people and created an occasion to ease escalating tensions over China's unilateral imposition of an air defence zone above a disputed part of the East China Sea.

"Happy 100 days to the baby panda. May the friendship between the Chinese and American people grow even stronger," Peng said in a video message.

The female panda was only the second cub born at the National Zoo to cross the 100-day line since the first pandas arrived in 1972 in the wake of President Richard Nixon's historic visit to China. Bao Bao was described as a "clear envoy of China-US friendship" by the Chinese ambassador to the US, Cui Tiankai.

"Many people don't realise it but there are actually two Chinese ambassadors in Washington: me and the panda cub at the National Zoo," Cui wrote.

US vice-president Joe Biden is due to land in Tokyo in the first stop of an official six-day trip to East Asia that will include Beijing and Seoul.

Talks are expected to be dominated by China's Air Defence Identification Zone (ADIZ), which overlaps one set up by Japan in 1969 and extends Beijing's aerial authority over a disputed group of islands known as Diaoyu in China and Senkaku in Japan.

The US openly challenged Beijing by deliberately flying two military B-52 aircraft through the ADIZ in contravention of Chinese demands that all aircraft planning to enter the zone had to provide identification and a flight plan.

Bao Bao is due to make her first public appearance in 2014 after receiving her final set of vaccinations and learning to raise her hind legs to crawl.

"We are thrilled to welcome this little cub, a cub who exemplifies both the common bond between our nations and the bright future of this magnificent species. It's a little too much for a little bear, but I think she's up to it," said Michelle Obama.