Police have warned residents in Essex to stay indoors after reports of a lion on the loose.
Essex Police said they were working with Colchester Zoo experts after viewing what they believed was a genuine photograph of the lion, which was seen in fields near the seaside town of Clacton, north-east of London, on Sunday evening local time.
It is not yet known where the lion may have come from. Neither Colchester Zoo nor a circus that had been in the area said they were missing any big cats.
A witness, Rich Baker, 39, told the Daily Mail:"A man started running towards us, yelling: 'It's a f---ing lion!'
"He looked so panicked you knew it was not a joke. The lion, you could see it from the side. I grabbed my children's hands and we ran towards our caravan. My children started to scream, 'Daddy, is the lion going to get us?'
"It was 1 million per cent a lion. It was a tan colour with a big mane, it was fully grown, it was definitely a lion. It was just standing there, it seemed to be enjoying itself."
Another resident, Che Kevlin, told the BBC: "I heard a loud roar at 10pm. It sounded like the roar of a lion.
"It was worrying as we had just been for a walk with the dog. We saw the police helicopter but thought it was just searching for a person. It sounded like the roar of a lion. We have field and wood just behind our fence, so you never know."
Police have enlisted the help of specialist firearms officers as two police helicopters searched the area where the lion was seen. The search would continue through the night despite no sightings in the past few hours, a police spokesman told the BBC.
"Officers have spoken to the circus and confirmed that they do not have an animal missing, nor do they have any lions," the spokesman said.
Publican Dave Sparks of the Red Lion pub in St Osyth said the lion sighting was "the talk of the pub".
"We initially thought that it was a hoax but now we realise that it's genuine. The police are taking it very seriously," he told The Guardian.
"It's the talk of the pub. There have been a few people in here with children who have been quite worried but generally we are not too concerned."
A fake @EssexLion Twitter account has already been set up and has more than 19,000 followers. Another account, @TheEssexLion, has more than 1000 followers.
FOUND SOMEWHERE TO HIDE.GEEZERS INSIDE HIGH AS A KITE THINK I'M AMY CHILDS.TIME TO CRASH. WILL ENJOY THEM AS BREAKFAST WITH A CAN OF MONSTER — Essex Lion (@EssexLion) August 27, 2012
you only lion once — Essex Lion (@TheEssexLion) August 27, 2012
In November, passengers were forced to remain on a train for two hours at Shepley station in Yorkshire after a woman reported seeing a lion, The Guardian reported then. No lions were found.
In May, police launched a major search after a white tiger was seen in a field near Hedge End, Southampton, in Hampshire. The animal turned out to be a life-sized stuffed toy tiger.