Although mainly bright blue, they range from deep purple to white

Tourists are being warned about cauliflower jellyfish, sometimes called sea nettles, lurking in the waves or even landing ashore.

Officials in West Mersea and Southend say hundreds have been washed up on the beaches over the last few days.

Dozens of people have already been stung - as the hot weather increased the jellyfish numbers.

David Knapp, of Southend Sea Life Adventure, said the sting felt similar to being pricked by a nettle - hence the nickname.

Although mainly bright blue, they can also be deep purple, beige and white.

Hundreds have been washed up at Southend and West Mersea

Mr Knapp said the jellyfish, which can grow to the size of a small dinner plate are often found in the Thames Estuary.

"Fishermen have reported large swarms. They are becoming more and more commonplace," Mr Knapp said.

He believes cleaner water in the estuary and sudden heatwaves earlier in the year are contributing to the growing numbers.

Anyone who is stung should apply anti-histamine cream, vinegar or even urine as a neutraliser, he said.

Sea nettles' hanging tentacles can grow to five metres while being almost invisible.

It fishes the sea by swimming, letting its tentacles out and drawing them in again to eat the catch.