Photo

The giant panda Mei Xiang while giving birth at the National Zoo in Washington on Saturday.Credit Smithsonian's National Zoo, via Reuters

Panda lovers, rejoice. Mei Xiang, a giant panda at the National Zoo in Washington, gave birth to healthy twin cubs on Saturday, just three days after the zoo’s staff discovered that she was pregnant.

The first birth, at 5:34 p.m., was broadcast live online on the zoo’s Panda Cam and announced on its official Twitter account. The second birth, at 10:07 p.m., was unexpected and was announced on Twitter. The announcement included a picture that appeared to show the cub being examined by veterinarians.

“It appears healthy,” the zoo said on Twitter.

Mei Xiang is a minor celebrity in Washington, and her breeding is watched closely by panda fans around the world. Giant pandas mate infrequently, and the birth of a healthy cub is uncommon. Mei Xiang has never before given birth to more than one healthy cub at a time. Bao Bao, one of her cubs who was born in 2013, was followed a day later by a stillborn sibling.

Besides Bao Bao, Mei Xiang has had only two cubs who survived: Tai Shan, who was born in 2005, and a cub who died in 2012 shortly after its birth.

On Saturday, people could watch live online as she gave birth to the first cub, which happened 30 minutes after her water broke as she lay on her back in a narrow cage.

“It doesn’t get old for us,” Laurie Thompson, a zoo official, told reporters on Saturday. “We’re very excited to share this with you guys, our new cub.”

Ms. Thompson, speaking before the second birth, said the mother and the first cub were “doing really, really well.”

The zoo said it expected that Mei Xiang would spend the next one to two weeks in her den bonding with the cub. Veterinarians do not expect to examine the first animal for several weeks, they said. Its sex will be determined at that time.

Zookeepers were not sure Mei Xiang was pregnant until they discovered a four-centimeter-long fetus during an ultrasound procedure Wednesday morning. At the time, the zoo predicted that the cub would be born between Aug. 28 and mid-September, but also warned that there was “a substantial possibility” that Mei Xiang could “resorb or miscarry” the fetus.

Those warnings, however, appeared to be for naught on Saturday. Not only was one cub born, but two. The zoo said it would release more pictures and video of the first cub soon.

The National Zoo said on Wednesday that it did not know the identity of the cubs’ father. Mei Xiang was artificially inseminated on April 26 and 27 with semen from both Hui Hui, a giant panda who lives at the China Conservation and Research Center for the Giant Panda in China’s Sichuan Province, and from Tian Tian, a giant panda at the National Zoo.

Hui Hui’s semen was collected in China, frozen and flown to Washington, while zookeepers used what they called “high-quality fresh semen” collected from Tian Tian.

“A cub by Mei Xiang and Hui Hui would be very genetically valuable, helping to preserve the genetic diversity of the panda population in human care,” the zoo said in a statement Wednesday.

All of Mei Xiang’s previous cubs were sired by Tian Tian. Genetic testing will be done to determine the cubs’ father, the zoo said.