Greece has confirmed the first bird case after the emergence of positive results on eight dead birds found in the northeastern Evros river delta over the weekend.
According to state-run television as quoted by Sky News, tests for the deadly H5N1 strain of the flu are pending.
The news comes as British scientists travel to the Far East to help develop a global strategy to fight bird flu. It also follows a warning from the Chief Medical Officer that a Europe-wide pandemic is "inevitable".
Officials have feared the spread of the disease is likely because it also sits on one of the busiest migratory routes from Europe to Africa.
"Our operation is in full swing," Agriculture Minister Evangelos Basiakos has earlier told reporters. "We have over 1,000 vets and employees on duty at the moment. There should not be any panic. Our labs are working, the system is working."
In another main migratory route, Croatia had started testing dead birds found by citizens, becоming the latest country to begin testing birds after dead animals were found.
Bulgaria, which borders Turkey that confirmed H5N1 among domestic fowl last week, has tested scores of dead birds. But here officials said they had not yet found any suspected cases of the virus.
The virus found in birds in Romania and Turkey is the same deadly H5N1 strain that has killed 60 people in south-east Asia.
The infected farms have been sealed off and their birds destroyed but there are fears that wild birds may already be infected and could spread the disease as they migrate.