Washington zoo officials heralded the arrival of "a precious giant panda cub" Friday, following the much-watched birth of panda Mei Xiang's latest baby, four years after her last pregnancy.

The new mother was exhibiting typical panda mom behavior like "nursing her cub and cuddling it close," the Smithsonian's National Zoo said on Twitter.

"We're overjoyed to share that Mei Xiang gave birth at 6:35 pm and is caring for her newborn attentively," it said, adding that mom and cub "appear to be doing well."

Fans of the panda were able to follow her labor live thanks to a "panda cam" accessible on the zoo's website 24 hours a day -- although high interest caused the feature to crash at some points.

Mei Xiang, who is 22 years old, was artificially inseminated on March 22 with the frozen semen of Tian Tian, another resident giant panda who will turn 23 later this month, according to the zoo.

Giant panda Mei Xiang rests in her enclosure in August 2016 at the National Zoo in Washington. Photo: AFP

Since the two pandas' arrival in 2000, Mei Xiang has given birth to three surviving cubs: males Tai Shan in 2005 and Bei Bei in 2015, and a female, Bao Bao, in 2013.

The three were returned to China on their fourth birthdays under a partnership contract in which China owns the pandas.

Mei Xiang and Tian Tian themselves will be returned to China next December.

Under the US-China agreement, the National Zoo pays $500,000 per year towards panda conservation efforts in China.

Genetically similar to the bear, pandas feed exclusively on bamboo. They weigh in at approximately 220 pounds (100 kilograms) and measure up to six feet (1.8 meters) long.