Tens of thousands of jellyfish-like creatures have washed up on beaches on New Zealand’s South Island.

Axar.az reports citing The Telegraph.

The velella, which is related to jellyfish and also known as by-the-wind-sailors, blanketed patches of beaches on the island’s west coast, the Greymouth Star reports.

They covered an area of 18 x 4 meters on one beach and soon began rotting in the sunshine, exuding a strong smell.

Conservation officials say it is common for the jelly creatures to wash up in the spring as water temperatures rise, but added they were surprised by the vast number.

“It’s very unusual that you have so many thousands of them washed up in one place,” the country’s Department of Conservation (DOC) said.

“It’s a common species around the west coast and around NZ and they do wash up, usually in tens or hundreds.”

DOC marine specialist Don Neale told the New Zealand Herald it is common for marine life to wash up more frequently over the spring months.

“As the sea starts to warm up in the spring, all the floating plankton starts to bloom and it’s not unusual to get a lot more things like this starting to wash up, as well as ‘red tides’ plankton out at sea,” he said.

The website jelly watch explains they are “not dangerous to humans”, but says “they can sting and capture small prey”.

“Velella typically live far offshore in open ocean waters, and their little sails help distribute them using the force of the wind,” it adds.

“However because they sail only downwind or at a slight angle to the wind, they are often blown ashore in very high numbers, with millions piling onto beaches in drift rows.”

Last year, a mysterious object that washed up on another New Zealand beach divided opinion.