National Zoo has new baby panda

National Zoo panda Mei Xiang gives birth Friday afternoon. Gender and size of the new National Zoo panda are not yet known. 

A giant panda gave birth at Washington's National Zoo on Friday, causing a buzz among fans as they flocked to a panda cam's live feed to hear the cub squeal and watch the mother immediately start caring for it.

The zoo said Mei Xiang gave birth at 5:32 p.m. Friday, two hours after her water broke. Zoo officials said the panda team heard the cub vocalize and that the mother picked it up immediately and began cradling and caring for it.

"WE HAVE A CUB!! Born at 5:32 p.m. this evening," the zoo tweeted.

"I'm glued to the new panda cams and thrilled to hear the squeals, which appear healthy, of our newborn cub," said Dennis Kelly, director of the Smithsonian's National Zoo.

Fans of the 15-year-old panda who had been tracking her suspected pregnancy on a Giant Panda Cam flocked to the live feed.

With the zoo heralding the cub's birth on Twitter, the pandas' excited fans responded in kind. Congratulations poured in under the hashtag "cubwatch," including hopes that this year's cub would survive. "Last year was so heartbreaking," as one person tweeted, while another said, "Good luck, little Butterstick 2 !!!"

Mei Xiang had previously given birth to two cubs. Tai Shan was born in 2005 and a week-old cub died last September.

Panda cubs are especially delicate and vulnerable to infection and other illness. They are about the size of a stick of butter at birth. The first weeks of life are critical for the cubs as mothers have to make sure they stay warm and get enough to eat.

Zookeepers said at a news conference on Friday night that giant pandas give birth to twins 50 percent of the time, so they will continue to keep an eye on Mei Xiang for 24 hours.

Brandie Smith, curator of mammals at the zoo, said Friday night that mindful of last year's loss, zookeepers will be more hands-on with this cub.

"We know that Mei Xiang is an excellent mother," Smith said. "When she has a cub, she will take care of it."

Smith said that will zookeepers don't want to disturb the bonding between the mother and cub, but they will take the risk and do an assessment of the cub within the first 48 hours.

The biggest concern is the cub's weight, Smith said, and that it continues to gain weight. Zookeepers will also be listening for healthy squeals from the cub, and signs and sounds that it is nursing.

The panda team will perform health checks every few days. Its gender was not immediately known.

Mei Xiang is expected to spend almost all of her time in her den for the next two weeks with her new cub.

The zoo has been on round-the-clock panda watch since Aug. 7, when Mei Xiang began showing behavioral changes consistent with a pregnancy or pseudo-pregnancy.

A Chinese panda expert performed artificial inseminations on Mei Xiang on March 30 after she failed to breed naturally with male panda Tian Tian.

Zookeepers had not been certain that Mei Xiang was pregnant, because she refused to cooperate with attempts to perform an ultrasound.

The David M. Rubenstein Family Giant Panda Habitat, which has been closed to the public since Aug. 2, will remain closed to provide quiet time for Mei Xiang and her cub.