Six piglets cloned from an animal famous for surviving more than a month trapped under the rubble of the Wenchuan earthquake are developing at a steady pace, say scientists.

Six piglets cloned from "Strong pig".

Du Yutao, who is leading the project, said the piglets are lively and growing day by day at the Beijing Genomics Institute's experimental base in Huizhou, Guangdong province.

"After several weeks of being taken care of by the staff here, each piglet weighs more than 6 kilograms," the doctor told China Daily on Monday.

The animals' father - nicknamed Zhu Jianqiang, or strong pig, after the 2008 disaster in Sichuan province - is unable to reproduce naturally. To help out, scientists collected cells and took them to the institute's headquarters in Shenzhen on Feb 16 for further study.

After breeding the boar's fiber cells, technicians used manual technology to clone his embryos, which were then successfully implanted in two healthy sows on May 12 this year, the third anniversary of the Wenchuan earthquake.

The surrogates gave birth on Aug 31 and Sept 2 respectively, with the heaviest piglet just 1.6 kg at birth, Du said.

"The clones are no different from common piglets in appearance, although clones are usually thinner and have weaker constitutions," the doctor said, adding that each piglet has a black birthmark between their eyes and bears a striking resemblance to Zhu Jianqiang. Residents and tourists cannot yet see the animals, as the experimental base is not open to the public.

China has cloned many animals in recent years, but it is the first time piglets have been reproduced from a boar older than 5, which is equivalent to a 60-year-old human, Du said.

Zhu Jianqiang, who is now cared for in a museum in Sichuan, emerged from the rubble after being buried 36 days. The 150-kg boar reportedly survived by chewing charcoal and drinking rainwater.