Families fled a beach after a shark was reportedly spotted off the Kent coast on Tuesday.
Eyewitnesses pictured what appeared to be a dark tail fin lurking just 150ft from shore as children played in the water.
The alarming sight was seen by two boys who hollered “is that a shark?” before running down the beach at Warren near Folkestone.
Emma Horne was at the popular spot, just 10 miles from the cliffs of Dover, and began filming the giant fish - believed to be a basking shark.
The receptionist was with her children Finley, seven, and Alby, five, when she spotted the fin in the sea.
She took footage of the shark which emerged from in the water at 7pm.
She told The Sun : “We couldn’t believe it. The boys were playing in the water so I got them out quickly.
“There were two young boys who spotted it and were clearly scared — they ran away and one of them shouted, ‘is that a shark?’.
“I warned people and a woman quickly called her dog out of the sea. She was worried."
Her children were playing with nets, but were told to get out of the water before watching the shark from afar.
The kids were excited about the shark and questioned if it could be caught by them.
Wildlife experts believe the dark shadow which emerged near the cost was a basking shark.
The species if often seen in UK waters during warmer weather, but they are not of any danger to people and mainly off plankton.
Folkestone Rescue said Red flags have been put up at Sunny Sands and the Warren, due to a suspected sighting of a basking shark off shore.
Chris Lightwing said on its website said: "As a precaution, we are advising that people do not swim at these locations for 24 hours.
"Basking sharks are very large fish which feed off plankton, and are not considered dangerous to people or animals.
"Basking sharks have occasionally been seen off the Kent coast over the past few years.
"While the risks are usually low, you should still keep your distance from any marine animals you may see while at the coast, including basking sharks, which are an endangered species."
Steve Harris, boss of fishing firm Dentex Charters confirmed the sighting was a shark.
Earlier this month, it was reported that another shark was spotted off the UK coast.
The blue shark was seen lurking in ankle-deep water at a popular beach near Falmouth, Cornwall.
Experts urged people to stay away, saying the sighting is a "real worry" with the species not usually venturing so close to the shore.
Harry Gooby, who filmed the shark, said the beast appeared to try and beach itself as it thrashed through the shallows.
"Silently, slowly and elegantly this blue shark just sort of swam by," he told BBC Radio Cornwall.
"Its snout came out of the water and onto the beach. It almost nuzzled underneath its neck on the beach."
Harry said he feared the shark was "in a bit of trouble but he was fantastic."
The eyewitness's concerns were quelled after speaking with a fisherman who did not think the fish was struggling.
However, experts say they are worried about the unusual sighting and fear that the shark could be hurt.
Dan Jarvis, of the British Divers Marine Life Rescue charity, advised people to ignore the sea creature and give it a wide berth.
