The 80-year-old was speaking on a visit to Hong Kong to promote her Roots and Shoots initiative, a project aimed at raising awareness of conservation issues among young people in 138 countries.

But Goodall said she wouldn't go to see the animals herself.

"I don't want to go and see them," said Goodall, whose methods scientists once criticised when she gave names instead of numbers to the chimpanzees she observed.

"I have enough nightmares without having to go there and see for myself," she said. "Sometimes I wish I didn't know all the things I do. It keeps me up at night."

Goodall's concerns about the orang-utans in captivity in the city echo those of a number of animal-rights activists who have criticised the Leisure and Cultural Services Department for allowing animals to be kept in facilities they describe as depressing and cramped, and that appear to be 50 years old.

"Their cages are so barren and it's built like a menagerie from Victorian times, a style we know now to be hell for the animals," SPCA chief veterinary surgeon Dr Jane Gray said.

Gray and Mara McCaffery, founder of the Hong Kong-based Orang-utan Aid, have complained for years that the highly intelligent primates are not getting the intellectual stimulation they need and that they appear to be miserable.

While some activists believe zoos are universally inhumane and should be closed, Goodall stressed that animals could be happy in captivity at a "good zoo", provided considerable funds went into infrastructure and care and the animals were kept intellectually stimulated.

However, neither the zoo nor Ocean Park, which keeps dolphins, make that grade.

"Any zoos with dolphin shows are wicked," Goodall said. "As long as it has dolphin shows, it is not a good organisation."

Watch: Hong Kong zoo under fire for "outdated" facilities