Two suspected cases of foot-and-mouth are being investigated, the UK's chief veterinary officer has said.
Honeychild Manor Farm in Kent has been sealed off
Debby Reynolds said a control zone had been set up around a farm in Romney Marsh, Kent. Cattle have been tested and results are awaited.
A second new control zone is centred around Chessington World of Adventures theme park in Surrey.
It is outside the restricted zone imposed in Surrey earlier this month after the outbreak was first detected.
In a statement, Chessington World of Adventures, which incorporates Chessington Zoo, said it had called in vets and alerted Defra following concerns over one of its sheep.
A spokeswoman said: "As a precautionary measure and because of the high state of alert currently in place due to the recent cases of foot-and-mouth disease, it was decided to immediately check all our cloven hoof stock for any signs of disease and do necessary tests."
She also said that the calling in of Defra was done "purely as a precautionary measure to ensure the well-being of the animals and protect the local community".
"There is no reason to suspect that anything but a full clearance will be received from Defra. We will obviously continue to take the advice given by both Defra and our own dedicated vet."
The Children's Zoo and Creature Features attractions are closed to the public, but the rest of the park and zoo remain open, she added. The zoo at Chessington celebrated its 75th anniversary last year.
Three cattle at the Kent farm have been tested after "an inconclusive assessment of clinical symptoms" of the disease.
A 3km (1.8 mile) temporary control zone has been put in place around Honeychild Manor Farm in the village of St Mary in the Marsh.
Dr Reynolds said the test results were expected by the end of Tuesday or early Wednesday, but said the two new farms presented "a very low level concern".
She said the case in Kent was similar to one in Dorking, Surrey, last week, which turned out to be a false alarm.
A spokeswoman for Defra said: "We're being ultra-cautious at this point. There's a continuing need for relentless vigilance in response to foot-and-mouth disease."
Environment Secretary Hilary Benn said the new investigations showed "we are not out of the woods yet".
Farmer Steven Furnival, who runs the farm of 300 dairy cows in Kent, said he noticed some calves with unusual lesions on the muzzles of their mouths.
"Due to the current situation, I felt it was prudent to notify the authorities immediately," he said.
"Samples have been taken and sent away for testing. All we can do now is wait until we get the results, which we sincerely hope will be negative."
This is the first suspected case outside Surrey during the outbreak.
HOW FOOT-AND-MOUTH SPREADS
Direct contact, from animal-to-animal
Fluid from an infected animal's blister; saliva, milk or dung also pass on the disease
Animals eating infected feed
Virus can be spread by people or vehicles, if not disinfected
Airborne spread of disease also possible
Animals can begin spreading virus before visible signs of disease emerge
Minister for the South East Jonathan Shaw said the farmer involved should be congratulated for his vigilance.
"We have also moved swiftly as we have done throughout this process and the temporary control zone will allow us to be precautionary while we wait for the lab results to come back," he said.
"There is no need to panic at this stage."
Meanwhile, Culture Secretary James Purnell has announced a £1m aid package for the tourist industry, after it was hit by flooding and foot-and-mouth.
Foot-and-mouth was confirmed in a herd of cattle at Woolford Farm in Surrey on 3 August. A second case, at a farm nearby, was confirmed on 7 August.
A 3km (1.8 mile) control zone and a 10km (6.2 mile) surveillance zone are still in place around those farms.
Tests on a third suspected case within the zone, where cattle were culled, proved negative, as did those on a fourth possible case also in Surrey.
The government is awaiting the results of independent tests on soil taken from the original outbreak site at the Pirbright laboratories.
A review of biosecurity arrangements at Pirbright, led by Professor Brian Spratt of Imperial College London, is also awaited.
When the outbreak began, a nationwide ban on movements of susceptible animals was put in place.
Some restrictions have since been lifted, but many movements of livestock - such as sending animals to market - are still banned in England.