British police on Monday deployed firearms officers and a helicopter as they launched a lion hunt following reports of a cat-like beast roaming in a field in Essex.

"The large cat, believed to be a lion, was seen in fields off Earls Hall Drive in St Oysth, near Clacton, just before 7pm on Sunday," an Essex police spokesman said.

Residents living in the area are being advised to stay indoors.

Officers from Essex Police have been working with experts from Colchester Zoo who believe the reports to be genuine after being shown a photograph from a member of the public.

"There is an increased police presence in the area, including firearms officers and the police helicopter searching near where it was spotted," the spokesman said.

The helicopter's thermal imaging camera was also used, the spokesman told AFP.

Mystery surrounds where the lion might have come from. Police ruled out Colchester Zoo as all its animals were accounted for. The Great British Circus was based at Clacton Airfield but its run in the area ended around a fortnight ago, according to a local events website. Anyone who sees the lion is advised to call 999.

Roger Lord, of Earls Hall Farm, St Osyth, said a picture of the suspected lion had been taken by residents in caravans on the farm land and passed to police.

"The first thing we knew about it was a phone call from the police last night," he said. "I am sceptical - I think it might just well be a large domestic cat but they certainly saw something that they were were concerned about and they went down the right route to the police.

Che Kevlin said he heard what he believed to be a roar whilst out walking his dog last night.

"I heard a loud roar at 10pm. It sounded like a lion," he told the BBC. "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 a field and wood just behind our fence, so you never know."

Police are taking the hunt for the creature seriously, but many are seeing the lighter side, with lion spoofs and jokes circulating the internet.

At least two parody Twitter accounts for the lion have already sprung up under the handles @EssexLion ("Roar bruv, I'm a lion, ain't I?") and @TheEssexLion ("in your garden").

Elsewhere on Twitter, many were joking about the lion being let loose on the cast of popular British reality show, The Only Way Is Essex.

Other users claimed the lion had taken refuge in the Ecuadoran embassy in London, where WikiLeaks founder Julian Assange has claimed asylum. David Schneider wrote under the handle @davidschneider: "This is getting interesting. The Essex Lion has just taken refuge in the Ecuadorian (sic) embassy."

[Image via Agence France-Presse]