LONDON (Reuters) - British police have issued warnings after a spate of creepy clown sightings across the country, mimicking a prank that began in the United States and has spread across the world.

Police forces said they had received dozens of reports of "killer clown" sightings in the last week where individuals dressed in clown outfits sometimes carrying knives have acted suspiciously or chased people, often young children.

"We believe this to be part of a much larger prank which is currently sweeping across the USA and parts of the UK," said Sergeant Mel Sutherland from Durham Police in northern England.

The clown sightings started around Greenville, South Carolina, in August, when police received reports of clowns standing silently by roadsides, near laundries and trying to lure children into the woods with bags of cash and green laser lights.

It is unclear what started the craze, although some have suggested it may be part of a horror movie publicity stunt or an elaborate hoax, and there have been similar reports sightings in Australia and New Zealand.

The incidents in Britain have been harmless but nonetheless frightening, police said. In Durham, four children aged 11 or 12, were followed to school on Friday by a man in a clown outfit who was armed with a knife.

"It is very alarming he was carrying a knife however we do not think he intended to harm the children and as far as we are aware, this is part of the prank," Sutherland said.

Thames Valley Police, which covers an area from the west of London to central England, said on Sunday it had been called to 14 spooky clown incidents in the previous 24 hours.

In Clacton-on-Sea to the east of London, police said two girls were approached by two clowns asking if they wanted to go to a birthday party and that there had been a number of similar sightings in the area mostly near schools.

The recent craze led best-selling U.S. horror author Stephen King, whose 1986 novel "It" tells the story of a supernatural being that appears as a clown, to appeal for anti-clown sentiment to be tempered.

"Hey, guys, time to cool the clown hysteria - most of 'em are good, cheer up the kiddies, make people laugh," King wrote on his Twitter website last week.

(Reporting by Michael Holden, editing by Elizabeth Piper)