Bathers are being warned to watch out for venomous jellyfish, which have been spotted in increasing numbers along South Shore beaches.

A government spokesman said that the Portuguese man-of-war can deliver an extremely painful sting and should be avoided.

The jellyfish can be identified by their bluish/purplish gas-filled float on top of the water.

Their in-water tentacles are often not seen, making them a deadly predator for small fish and extremely painful for humans.

The spokesman advised that people should keep their distance and avoid touching them even if they wash ashore, as the tentacles can still be very venomous.

Those who do suffer a Portuguese man-of-war sting are advised to:

• Keep bystanders away and, using gloves, look for the trailing stinger or tentacles

• Remove the tentacles, along with the animal itself if still attached, and wash the affected area with seawater to wash away any tentacles

• Cover the area with shaving foam, and scrape the foam off using a blunt spatula

To inactivate the stingers, soaking the area in vinegar for five to ten minutes is recommended.

To treat the pain, use hot packs on the affected area for 30 minutes and consider placing the victim under a shower or running water “as hot as tolerable”.