A horse rider says she was chased by wild boar roaming free in forestry on the Wales-England border.
Carla Edmonds was chased by the boar while out riding
Around 20 boar are thought to be living in woodlands which straddle Monmouthshire and Gloucestershire.
Carla Edmonds, who lives near Monmouth, said she and her dogs were chased while riding in 3,500-acre High Meadow Woods.
Pig breeders in the area are also concerned that the animals - which may have escaped from captivity - could pass disease on to their herds.
Countryside users said their horses and dogs had been pursued by the beasts, which have razor-sharp tusks.
Nobody is sure where the boar, which can weigh up to 400lb, came from, though there have been reports of one breaking free on the way to an abattoir in Gloucestershire.
"It was absolutely astonishing," she said.
"I was riding along one of the paths in the forest, about 100 yards or so from the main road, and I saw a group of 20 or more.
"At first I couldn't make out quite what they were, but then I could see they looked like pigs."
Ms Edmonds' dogs began barking and her horse became agitated. The herd of boar gave chase.
"I could see them charging at a huge pace," she said.
She said her horse was seriously disturbed by the experience and took a long while to calm down.
Ms Edmonds took this picture of a boar living near her home
Other horse riders have had similar experiences, she said, with one taking a quad bike escort with her when entering the forest.
She claimed another villager was trapped in her home when wild boar blocked her lane.
"Something really needs to be done before someone gets hurt," Ms Edmonds said.
"My horse was seriously spooked, but I was able to control him, but a less experienced rider could have had a terrible accident.
"These wild boar are obviously a menace."
Pig breeders in Wales are particularly concerned by the reports.
Helen Tongue, chairman of the Wales and Border Counties Pig Breeders' Association, called for the herd to be rounded up.
"Wild boar are a danger to human beings and to animals, too," said Mrs Tongue, who farms at Devauden, near Chepstow.
Wild boar facts
A fully-grown adult boar can weigh up to 400 lb (180kg)
They can measure 6ft (2m) from snout to tail
Male boars grow tusks after they reach two years old
They have much bigger litters than domestic pigs, and can breed twice a year
Their diet can include mice, birds' eggs and lizards
"They can be extremely aggressive and have strong tusks which can do a lot of damage.
"I wouldn't be happy if they were wandering around anywhere near my home.
"There are so many pig diseases which can be easily transmitted.
"The regulations on moving pigs these days are extremely tight, to prevent the spread of disease, but these wild boar, roaming freely, could pose a serious disease risk.
"They are extremely strong animals, too, and can knock down fences easily, so they would have no problem getting into a farm where normal pigs were being kept.
"These animals need to be rounded up and sorted out before it is too late.
Anyone who sees them should report them to the police immediately, and anyone who has had any escape from captivity should have told the authorities, too."
Phil Glanville of Monmouthshire Council Trading Standards department added: "The local authority is making inquiries to try to find out where the wild boar have come from."