The bird flu outbreaks in Britain and the Netherlands may have been brought to Europe by wild swans migrating from Asia, the European Commission has said.
Millions of farm birds in South Korea were destroyed after an outbreak of the H5N8 bird flu earlier this year.
The European Commission said: "A species of wild swans might be carrying the virus without showing signs of disease."
The European Union has praised the Dutch and British responses to outbreaks of bird flu in both countries.
A EU spokesman said: "We can say that all the protocols were followed and we can only praise the behaviour of the authorities of the two member states."
The European Commission has introduced emergency measures after the H5 strain of the virus was confirmed at a duck breeding farm in Yorkshire and the H5N8 strain at a chicken farm in Utrecht.
Authorities are investigating whether there is a link between the outbreaks.
Emergency measures, including restrictions on the sale of live poultry, eggs and other poultry products, have been announced by the European Commission in the wake of bird flu outbreaks in Britain and the Netherlands.
The move comes after the H5 strain of the virus was confirmed at a duck breeding farm in Yorkshire and a recent outbreak of H5N8 at a chicken farm in Utrecht.
Other EU member states and non-EU countries, as well as international organisations, have also been informed.
The measures also include culling of poultry on affected holdings, the establishment of protection and surveillance zones, the introduction of sanitary measures (cleaning and disinfection).
A European Commission spokesman said: "The measures aim at quickly bringing the disease under control and at preventing the spread of the highly pathogenic avian influenza within the affected member states, to other member states and to third countries while minimising the disturbance to trade."
Chicken and turkey remains safe to eat, the Secretary of State for Environment, Food and Rural Affairs Liz Truss has told Parliament in the wake of a bird flu outbreak at a Yorkshire duck farm.
Asked whether consumers seeking to order Christmas birds such as turkeys would be affected, Ms Truss said: "Let's be clear, the Food Standards Agency have said it does not pose a risk for food safety for UK consumers - that's a very important point.
"The chicken and turkey people eat continues to be safe - this is a live animal disease."
"Early and swift action" is key to tackling the outbreak of bird flu at a duck farm in Yorkshire, Secretary of State for Environment, Food and Rural Affairs Liz Truss has told Parliament.
Speaking in the House of Commons, Ms Truss said a private vet reported the outbreak of bird flu at a duck farm in Yorkshire on Friday.
A Government vet visited the farm the same day following the report and the premises were placed under restriction.
Tests on samples taken at the farm in Nafferton confirmed the presence of H5 on Saturday evening but ruled out H5N1, she said. Investigations are ongoing into which particular strain of H5 the virus is.
Responding to questions, Ms Truss said: "We have seen a really good effort, I am clear we need to keep that up, to make sure we stamp out this disease - all of the experience of animal disease is it is important to take early and swift action and make sure it is stamped out."
A 6 mile restriction zone has been put in place around the Yorkshire duck farm at Nafferton close to Driffield where bird flu has been confirmed.
The zone bans movements of all poultry, products and waste within the area.
Current government guidelines stipulate that birds infected with avian flu are culled to prevent the spread of the disease.
Speaking to ITV News, a Defra spokesman said it was not clear whether the animals would be killed today, but preparations for the cull were underway.
6,000 ducks inhabit Lowthorpe Lane farm in the village of Nafferton, and they will all be killed following the confirmation of the outbreak.
Prof Andrew Easton, professor of virology at the University of Warwick, said:
The risk to the poultry industry is high and the current measures require that infected birds are killed as quickly as possible to stop spread to other flocks.
There is always concern that some strains of flu may be spread by wild birds and surveillance measures are also likely to be introduced in surrounding areas to check for the possibility of spread.
Nigel Gibbens, the government's chief veterinary officer has said the risk to the public from the outbreak of bird flu is "very low", and the public should not worry about the possible risk of it travelling through the food chain.
The outbreak of avian flu in a duck breeding farm in Yorkshire is "most likely" the same strain as the outbreak over the weekend in the Netherlands, ITV News understands.
The particular strain of the virus - believed to be H5N8 in Yorkshire, the Netherlands and Germany - is extremely contagious between birds, raising fears that there will be more cases in Europe.
If confirmed as H5N8 it will be the first time this strain has been found in Europe - having previously only been in Japan and Korea.