The giant panda cub born on Friday at the Smithsonian's National Zoo in Washington appears to be in good health after the zoo conducted a quick physical examination on Sunday morning.

"All the external features looked perfectly normal, so the cub has been described as vibrant, healthy and active," said Pamela Baker-Masson, a spokeswoman for the zoo. "My colleagues were very, very happy. This is joyful news."

The zoo tweeted the news on Friday, saying: "We have a cub!! Born at 5:32 pm this evening."

The abrupt delivery on Friday was caught by the zoo's webcam, which runs 24 hours a day, seven days a week. It showed the cub's mother, Mei Xiang, scooping the tiny cub up and then cradling it against herself. Baker-Masson said the mother panda Mei Xiang was agitated when the cub was taken away for examinations, pacing and growling in her den, but she calmed down immediately after it was returned and went back to cradling the cub.

After the birth, zoo officials kept a close watch on Mei Xiang throughout the night since nearly half of giant panda births result in twins. Twenty-six hours after the birth of the first cub, a stillborn twin cub did in fact arrive.

Mei Xiang was impregnated by artificial insemination by a Chinese panda expert in March. The donated sperm came from Tian Tian at the National Zoo and a panda named Gao Gao at the San Diego Zoo.

"It is not known who is the father yet," said Christine Kohl, a volunteer of the Asia Trail of the National Zoo, on Sunday outside the Giant Habitat, which had been closed to visitors since Aug 2 to create a more favorable environment for Mei Xiang's pregnancy.

Throngs of visitors to the zoo on Sunday were only able to see Tian Tian, while they were able to observe Mei Xiang and the newborn cub via webcam.

Giant pandas have been stars at the National Zoo, where local transit cards bear the image of a panda and local panda lovers say they are enjoying the pandamania.

Mei Xiang has given birth to four cubs at the National Zoo. The first one, Tai Shan, born in 2005, was a sensation, but it was returned to China in 2010. According to an arrangement with China, newborn cubs from parents on loan belong to China.

Mei Xiang gave birth to a cub in September, but it died after six days. Kohl said Mei Xiang grieved for days after the passing.

She said a Chinese expert was on site to offer help at last week's birth. The National Zoo has also sent its staff members to receive training at the giant panda breeding center in Sichuan province.

Usually a panda cub stays with its mother for 18 months, at which point the mother starts to push the cub away, Kohl said.

Since it takes months before it's determined if a newborn panda will survive, the new cub has yet to be named, Kohl said.

About eight years ago, Tai Shan was given his name 100 days after his birth. The name was chosen through an Internet vote of 202,000 people from around the world and comes from the name of a famous mountain in China's Shandong province. It is also the Chinese translation of Tarzan, the fictional character created by Edgar Rice Burroughs.

Agencies contributed to this report.

chenweihua@chinadailyusa.com