A blue dragon, a small but highly venomous type of sea slug, has been found on Karon beach in Phuket, according to pictures posted on the Monsoongarbage Thailand Facebook page.

The creatures are usually found in the middle of the sea and rarely seen in coastal areas, said Thon Thamrongnawasawat, a lecturer at Kasetsart University, in response to questions from the Facebook page.

In the case of Phuket, it might have been swept ashore by sea waves, Mr Thon said.

The blue dragon is a type of mollusc or sea slug known as a nudibranch. It feeds on other sea creatures, including the Portuguese man o’ war. It can sting as defence against predators.

The small creature rarely grows larger than 4 centimetres, but one sting can lead to nausea, pain, vomiting and a severe rash.

Mr Thon said the blue dragon can be found on the surface of the Atlantic, Pacific and Indian oceans in temperate and tropical waters throughout the world.

Those stung by a blue dragon will feel as if their skin has been pierced by a needle coated with poison. They are advised to apply vinegar to the wound, the same way to treat jellyfish stings.