The 50-year-old woman, identified only as Lisa, had registered in the Wolong Giant Panda Protection and Research Center in Sichuan province as a volunteer, the official Xinhua News Agency said.
She was wearing gloves and feeding the panda bamboo on Tuesday morning when "suddenly, the panda bit into her thumb," Xinhua said.
"When she cried out, the cub became excited and gripped more tightly," it said. "Lisa finally managed to wrench herself free."
About 20 percent of the thumb had been bitten off, Xinhua said.
A man who answered the telephone at the center's administrative office said it had no comment.
The center has been recruiting volunteers since 2004 for stints that last from one day to more than a month, Zhang Hemin, the center's director, was quoted as saying. They can prepare food, feed pandas under supervision and clear the enclosure with the help of professional keepers, he said.
We've been trying to warn people. Pandas are not cute and cuddly. They are man-eaters. (In this case, woman-eater). But notice that the government of China is keeping expenses down by getting people to volunteer to feed the pandas? It's unfortunate that people who volunteer don't understand they are literally going to feed the pandas. In small tasty bits.