British Chief Veterinary Officer Debby Reynolds said cows in a second area of the southern England county of Surrey had shown "mild clinical signs of infections," announcing that a new 3-kilometer (1.8-mile) exclusion zone had been set up around a farm previously unlinked to the outbreak.
Though the case is unconfirmed, Reynolds said the outbreak was a "developing disease situation," renewing worries of a repeat of scenes in 2001, when 7 million animals were killed and incinerated on pyres. Britain's agriculture and rural tourism industries were devastated.
The new suspected case is around 15 kilometers (9 miles) away from two farms where cases have been confirmed and a third plot where cattle have been killed as a precaution.
The farmer at the site, near the village of Wotton, said he had called a veterinarian after noticing signs of illness in some of his calves, and because he had links with the area where the earlier outbreaks occurred.
"The vet was absolutely sure this was not foot-and-mouth," farmer Lawrence Matthews said.
He said he was awaiting the results of tests, expected later Friday, "and hopefully they will not show foot-and-mouth at this farm."
If the latest tests prove positive, it would suggest the initial outbreak was not contained, increasing the prospect the virus could infect herds across southern England.
"The containment and eradication of foot-and-mouth disease remains our priority," Reynolds said in a statement late Thursday night. "This is why we have moved swiftly to put in place a temporary control zone while we investigate this development."
Foot-and-mouth disease does not typically infect humans, but its appearance among farm animals can have a swift and possibly far-reaching economic impact - several countries have banned imports of British livestock and Britain has voluntarily suspended exports of livestock, meat and milk products and destroyed more than 570 cows since the outbreak was identified last week.