Where the beast came from is still a mystery, but authorities are taking no chances after some locals reported sighting near Clacton, Essex, in the London suburbs.
Daily Mail reported that a witness described onlookers screaming as they came face to face with the predator, others heard it roar as it prowled the area.
The tabloid quoted Rich Baker, 39, a van driver from Romford in Essex, saying, "It was one million per cent a lion. It was a tan colour with a big mane, it was fully grown, it was definitely a lion."
"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?'"
Residents of a village where a lion is believed to be on the loose have spoken of their fear after police launched a huge search for the beast.
Armed police and helicopters are searching for the big cat after it was spotted in fields near Clacton.
Two force helicopters and around 30 police officers were scrambled after locals reported the sighting. Officers were last night working with experts from Colchester Zoo to track down the animal.
They will try to tranquilise the creature if it is found. The animal is not thought to have come from the zoo as all their animals have been accounted for.
