British beachgoers have been issued a warning after a number of Portuguese man o' war washed up the UK coast.

A number of the jellyfish-like water prowler were seen on the Cornish coast in Sennen, Crantock and Longrock. One was described as a "monster".

The creatures, known for their massive size and alien-like features, pack a nasty sting that can be excruciatingly painful and cause welts on the skin. The animal, which can grow up to 20 metres long, have been increasingly found floating close to British shores, despite them usually hiding away in in tropical waters.

There have been documented cases of deadly man o' war stings due to an allergic reaction.

Sharing a photo on Facebook, The NCI St Ives, wrote: "Huge Portuguese man o' war plus many more washed up on Sennen Beach today. Please be wary if going into the sea as they could also be heading up our coastline. They pack a real good punch."

Amanda Duffin said she spotted "massive ones" on Longrock beach near Penzance.

"Dog walkers need to beware," she told CornwallLive. "Saw two massive ones within ten meters of each other."

Man o' war can't swim. They float around the oceans taken by currents and winds and can wash up in the UK following a storm. They are not jellyfish, and are instead a rarer creature known as a 'zooid'.

They can be spotted with a distinctive purple float, blue-purple tentacles, an pink-tipped crest. They can appear translucent after being washed ashore.

Matt Slater, the Marine Conservation Officer for Cornwall Wildlife Trust, said: "Portuguese man of war are capable of giving a painful and sometimes serious sting. Swimmers are advised to avoid them where possible. If stung wash the area affected with sea water and scrape away any tentacles/stinging cells with a credit card or similar. Then apply hot water to the area to denature the sting and seek medical advice from Lifeguards or GP. "

Another warning from coastguards was issued in Wales after strange creatures were seen on Porth Trecastell beach, near Caernarfon

"Visitors enjoying a swim earlier today at our local Porth Trecastell beach happened to come across what looks like a Portuguese man-o'-war washed up on the beach," Rhosneigr Coastguard said on September 16. "If it is an actual Portuguese man-o'-war then here's some advice... HM Coastguard issues warnings about the presence of the Portuguese man o' war on beaches, advising the public and dog owners to avoid touching them due to their extremely painful sting, even when the creature is dead."

Wildlife experts said the 'disco' animals are actually mauve jellyfish, which the Marine Conservation Society said made up 2.6% of all jellyfish sightings in the UK last year

Warning as deadly man o' war washes up on UK beach - The Mirror