A group of Siberian chipmunks that escaped from a country estate are "wanted dead or alive".
The omnivorous rodents could pose a threat to the English ecosystem
Thirty of the animals escaped from an enclosure at Wellington Country Park on the Hampshire/Berkshire border in May, BBC Wildlife magazine discovered.
It contacted the Department for Environment, Food and Rural Affairs (Defra) who said 18 were found dead days after the "break-out".
Eight were shot but the remaining four may still be on the loose.
The were thought to have already died but a camper claimed to have spotted one of them at nearby Riseley in September, according to Defra.
The Defra spokeswoman, referring to the situation as "quite worrying", added: "If anyone does see any more, we would encourage them to contact Defra as soon as possible to let us know.
"To our best knowledge, all the chipmunks (from Wellington Country Park) have either died or been recaptured.
"We are keeping a very vigilant eye on this particular case.
"Anything that enters into the English wild can upset the delicate ecosystem.
'Harmless to humans'
"They (chipmunks) are wanted: dead or alive," she added.
Defra has been hunting the chipmunks since June.
Park staff carry out daily patrols and have been setting traps to capture them - a procedure expected to continue until next Spring.
The stripy omnivorous creatures - although harmless to humans - could become a problem for bank voles and wood mice by competing for their staple diet including nuts, seeds and berries.
The rodents have also been known to eat chicks and eggs from birds' nests.
In statement, Wellington Country Park, which is no longer keeping chipmunks, said: "To be honest, I don't think many will still be alive.
"I think most of them have been trapped or killed by grey squirrels."
Seventeen chipmunks released at an amusement park in Brussels in 1980, bred in the wild. By 2000 their number had increased to almost 20,000.