A 25-year-old Brazilian woman said she is planning to lodge a formal complaint against the head of the Rio de Janeiro Zoo after one of the monkeys threw a stone at her during a visit.

Regiane Viana told O Dia newspaper that she was taken to the hospital and needed treatment after she was hit on the head by the monkey's stone.

She said she had already recovered from her injuries but is still shocked over the incident.

A spokesperson for the zoo told the paper, "It was unbelievable, the monkey threw a rock at this woman out of the blue.

"We never had this before, but we have to investigate and find out how he learn this trick, soon people will think not even Rio's zoo is safe anymore, even the animals are getting violent!"