CHENGDU, Aug. 17 (Xinhua) -- A female giant panda cub weighing 270.4 grams became the world's heaviest captive panda newborn ever registered, a panda research center in southwest China's Sichuan Province said on Wednesday.

Cuicui, a 16-year-old panda, gave birth to the cub at the Wolong Shenshuping panda base at 9:39 p.m. on Aug. 5, breaking the previous birth weight record of 249 grams held by a panda born in 2021, according to the China Conservation and Research Center for Giant Panda.

The cub's delivery process was worrisome as it took Cuicui a long time to exhibit any labor reaction after her water broke, according to Cheng Jianbin, Cuicui's keeper.

"We were all worried that she would have a difficult labor and that the cub could be in danger of an oxygen shortage," Cheng said. "Cuicui paced back and forth in the 'delivery room' and appeared agitated. Worried as we were, we could only monitor and observe her around the clock, waiting quietly and keeping her company."

The baby panda was eventually born nearly 40 hours after Cuicui's water broke.

"We didn't expect Cuicui to give us such a big surprise, giving birth to a 'heavyweight' baby," Cheng said.

The last time Cuicui gave birth was in 2018, and all her previous cubs weighed over 200 grams, Cheng said, adding that Cuicui is extremely maternal and very good at taking care of her young.

Wei Rongping, director of the Wolong Shenshuping panda base under the China Conservation and Research Center for Giant Panda, said the center selected pandas for breeding in March as spring is a typical mating season for the species.

As the pandas are entering their gestation periods one after another, their keepers are taking shifts around the clock to monitor the bears through cameras or on-site, offering timely analysis to ensure the smooth delivery and safety of the cubs, Wei said.

Since June, six pandas at the center have given birth to cubs. The center has welcomed 11 new cubs so far, with five pairs of twins. This birthing season is expected to last until the end of August.