Zoo visitors were shocked as three penguins began mating inside their enclosure.

Ariel Trinidad and friends were watching a colony of king penguins at Ocean Park in Hong Kong when three of the birds - a pair and their friend - engaged in breeding acts, on October 26.

Footage shows a female Antartic bird bending forward with her tummy touching the ground.

Her partner mounted her from behind while a third penguin guided him, supporting his back so he would not fall off balance.

Amused tourist Ariel, who was visiting the former British territory, said: 'They seemed to be having a threesome. We were amazed by how they went about it. It's not every day that we get to witness something like that.'

In some penguin colonies, helper males may be observed lingering near a mated pair. These males often guard the pair or assist with mate protection by preventing other males from approaching the female.

King penguins are the second-largest species of penguin after the emperor penguin. They are known for their striking appearance with black and white plumage and bright yellow and orange markings around their heads, necks, and chests.

While much of the infrastructure put in place by the British allowed Hong Kong to become a global financial centre, the country has slid back into authoritarianism since being returned to the Communist rulers of mainland China.