A man is in intensive care in a north Queensland hospital with facial stings after diving into an irukandji jellyfish.

The 29-year-old man is in a stable condition after being rescued by helicopter from a yacht moored off South Molle Island in the Whitsundays yesterday.

Mackay Base Hospital physician Dr Dale Hanson says irukandji are particularly dangerous because of their size.

"The nets are able to keep out the box jellyfish but the irukandji - which is quite a small jellyfish - can in fact get through those nets," he said.

"Generally the irukandji are about the size of your index finger. It's got a bell that's about one centimetre across and then one tentacle off each corner of the bell that's up to 10 centimetres long."