A giant panda in China has given birth to the heaviest cub born in captivity after the longest period in labor and elsewhere twin pandas each gave birth to twins, Xinhua news agency reported.

Six-year-old Zhang Ka delivered the baby on Monday at the Wolong Giant Panda Research Center in the mountainous southwest, Xinhua said.

The cub weighed just 218 grams (half a pound), but was still the heaviest panda ever born in captivity, where most cubs are born at between 83 and 190 grams, Xinhua said.

"It is very rare for them to be even near 200 grams," it said in a report late on Monday.

But the size and the fact that it was Zhang Ka's first meant a "painstaking and eventful" birth for the mother, who was born in the wild.

"The whole process lasted about 34 hours and was the longest in the history of panda reproduction," Xinhua quoted Zhang Hemin, head of the Wolong centre, as saying.

Both mother and baby were doing well, the agency said.

Two twin panda sisters, also aged six, gave birth to two pairs of twin male cubs -- with much less drama -- on Sunday and Monday respectively in the Chengdu Giant Panda Reproduction and Research Center near Wolong, Xinhua said.

It brought the number of panda cubs born in captivity in China so far this year to six, it said.

The giant panda is one of the world's most exotic and endangered species and is found only in China, where it is a national treasure.

An estimated 1,600 wild pandas live in nature reserves in Sichuan, Gansu and Shaanxi provinces.

It is extremely hard to breed giant pandas in captivity. Females only ovulate once a year, with a slim 24- to 48-hour window for breeding when artificial reproduction methods are usually adopted. Infant mortality is also high.

Pandas eat bamboo shoots and spend a lot of time sleeping. They usually wean their young at around 18 months, and healthy pandas live into their late 20s or early 30s.