A second case of foot-and-mouth has been confirmed at another Surrey farm, near the site of the first outbreak.
About 200 cattle have been culled so far
Ministry Defra said 102 cattle had been culled at the site, inside the 3km protection zone around the farm where the virus was confirmed on Friday.
Meanwhile Roger Pride, owner of the first herd to be culled, said he was "devastated". An overflowing sewer may have been a source, he suggested.
Inspectors are due to confirm the source of that outbreak later.
Meanwhile restrictions on movement have been relaxed in Scotland - animals will be able to be transported to slaughterhouses under strictly controlled conditions.
'Beyond our control'
In a statement, Mr Pride said he noticed last Thursday that his cattle were off-colour and drooling and called his vet - who advised him to contact Defra.
The following evening Defra confirmed the cattle had tested positively for foot-and-mouth, he said.
Mr Pride said Woolford Farm, near Guildford, had "the highest standards of bio-security" and no animals had been moved on or off the farm since early June.
He said he believed it was possible a sewer which overflowed into part of the field may have been the cause.
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, vehicles or roads, if not disinfected
Airborne spread of disease also possible
Animals can begin spreading virus before visible signs of disease emerge
"Whatever the cause of the outbreak, it is obvious that we've been the victims of circumstances far beyond our control," he said.
The official findings of a Health and Safety Executive investigation into the source were due to be handed to ministers at 1300 BST, but is now expected later.
The strain of the virus found was being used at both private vaccine manufacturer Merial and the government-funded Institute for Animal Health, both based on the Pirbright complex, four miles away.
One line of inquiry is that floodwater may have contributed to the accidental release of the virus from one of the labs. Both say they are confident in their bio-security measures.
On Tuesday, a Defra spokesman said laboratory results had confirmed an outbreak at the second site.
Environment Secretary Hilary Benn said vets had spotted the signs on Monday, and a swift decision was taken to cull the animals.
He urged farmers to continue to examine their stock.
A 3km (1.8 mile) protection zone and a surveillance zone with a minimum radius of 10km (6.2 miles) is in place around the first site.
Farmer Laurence Matthews, who owns the land where the second outbreak struck, said the farmer whose cattle were culled, and his family, were "absolutely devastated".
"We were starting to think that maybe this virus had been contained... now with this second outbreak this has set us back again," he told the BBC.
"Most farmers... are very, very scared and all activity on farms has almost come to a standstill."
The government says no decision has been taken on whether to vaccinate livestock, but 300,000 doses have been ordered from Merial - to ensure it is ready if needed.
The National Farmers' Union, which has opposed the use of vaccination in the past, said the government should have the capability to use it "as an option", depending on the circumstances.
NFU head of communications Anthony Gibson praised the response so far, saying: "I think that everything that could have been done, has been done. I think the lessons, so far, have been learned from what went wrong in the 2001 outbreak."
FOOT-AND-MOUTH IN NUMBERS
97 cattle were culled from the first outbreak - 64 from infected premises, 33 from neighbouring premises. 102 were culled in the second outbreak
111,000 farms across UK affected by movement ban
That includes 10m cattle, 23m sheep and 5m pigs
The government had banned the movement of all livestock across Britain - although some restrictions have now been relaxed in Scotland.
The European Commission has formalised a ban on British exports of meat, milk products and live animals.
Northern Ireland, which has imposed a ban on all cattle, sheep and pigs from Britain, has been excluded.
Sir Donald Curry, who headed an inquiry into the future of farming after the 2001 foot-and-mouth outbreak, said it was too early to lift the restrictions but it would soon be clear whether the "very virulent" disease had spread.
He added: "Provided the disease hasn't spread then within a few more days, government can consider relaxing other parts of the United Kingdom from the restrictions but we do have to be very certain."
He said that if livestock restrictions remained in place for weeks, "for many farming businesses this could be crippling".
"Hopefully this won't go on for weeks, the disease will be contained," he said.
This flood near Woolford Farm on Friday 20 July could be connected
There has been some criticism from some farmers, the Lib Dems and the Conservatives that footpaths inside the 3km protection zone have not been closed.
The government has said footpaths are closed on the infected premises, but others inside the zone remained open as veterinary risk assessments had shown the risk was negligible.
Defra said the countryside "remains open" to visitors.
The NFU has estimated the outbreak could cost "tens of millions of pounds", affecting not just farmers but related industries, such as abattoirs and meat packaging plants.
Defra has set up a helpline in response to the latest outbreak on 08459 335577.