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The sight of a blood red sea sparked panic at Chinese beaches.

Villagers were in fear after they woke up to find the sea had turned crimson overnight.

Disturbing pictures of red waves crashing onto the beach turned the coastline into a Jaws-like scene in Shenzhen, in China's Guangdong province.

Some villagers believed believed a swimmer had been killed by a shark or, perhaps, Judgement Day had arrived - as biblical texts forewarn that a blood red sea is one of the ten plagues of Egypt marking the End of The World.

But the actual cause turned out to be thousands of algae blooms, which change colour to a deep red or dark brown when they reproduce in one area in large numbers.

(Image: CEN) (Image: Barcroft)

Local environment official Kang Ts'ai said: "Although it is harmless, we have nevertheless slapped a ban on any swimming or watersports in the area until the algae is swept back out to sea."

As well as the ban on swimming, fishing was also banned.

Shenzhen’s Monitoring Centre for Marine Environment and Resources experts said that they expected the algae to disappear once the water temperature had lowered.

Algal blooms can occur in freshwater as well as marine environments .

And species may be recognised according to the discoloration of the water resulting from the high density of pigmented cells.

An Environmental Protection Agency report in 2013 found that changing environmental conditions such as more algae growth is associated with current climate change, and may negatively impact the environment, human health, and the economy for communities across the US and around the world.