The deadly Portuguese man-of-war has suddenly arrived off the Sussex Coast in the biggest-ever recorded invasion of its kind.

Hundreds of the slimy fish, which look like coloured jelly or an inflated plastic bag, have been washed up on beaches after being blown in from the mid-Atlantic Ocean on the south-westerly winds.

More than fifty have been officially reported on Brighton beach between the West Pier and the Marina, while hundreds more have been washed up on the shore from Worthing to Hastings.

It is the first time in living memory the poisonous fish, which have been known to kill swimmers with their huge tentacles that can dangle up to 20 feet in the water, have arrived off the Sussex Coast in such numbers.

At first glance they could be mistaken for blown up plastic bags with mushy, coloured sweets inside, but they have a nasty sting in their long tails.

When they sting it feels like a cluster of stinging nettles hitting the flesh.

Swimmers have been known to drown after suddenly getting entangled in the tentacles and panicking. Bathers have been dragged from the seas with whiplash-like marks across their bodies after encountering the fish.

Cornwall, Devon and Dorset beaches have reported invasions by the Portuguese man-of-war in the past, but they have never been seen off the Sussex Coast in such numbers.

They are normally found in the warmer Atlantic waters and in the Pacific, Indian and Caribbean oceans.

Their arrival prompted Brighton and Hove Council to warn anyone finding the fish not to pick them up and to report any sightings.

A spokeswoman said: "The advice is leave them where they are. Do not touch them and let the Seafront Office know where they are."

If the fish had arrived during the main bathing season, the council would have considered warning swimmers not to bathe off Brighton beaches.

Gerald Legg, keeper of natural sciences at Brighton and Hove's Booth Museum of Natural History, said it was the biggest invasion of the fish recorded off the Sussex coast.

"The numbers are extremely unusual. It is not down to global warming, but due to the recent constant south-west prevailing winds.

"They are passive fish which cannot swim and are purely driven by wind and current. They have just been blown here.

"They do have a nasty nip. I was stung by one today as I put it in a different tank. It felt like a very bad sting from a stinging nettle.

"People should not pick them up as they can still sting when dead after lying on the beach for several days."

The Portuguese man-of-war is so called because the gas-filled bladder, which acts as a float, is reminiscent of the hats worn by the Conquistador soldiers from Spain and Portugal who conquered America in the 16th Century.

Most specimens found on the beaches have their tentacles retracted into their gelatinous bodies.

The man-of-war is a deadly predator in its element. It traps small fish in its tentacles, often young herring. The larger ones sometimes even catch fish as large as mackerel and flying fish.

It stuns its prey with neurotoxins from its long, trailing tentacles, which render the fish paralysed. It then drags the fish into its stomach, which is located on the underside of its floating gas bag and digests it.

People who are stung are told to remove tentacles with tweezers or matchsticks and rinse the sting with salt or fresh water and apply ice for pain control.