Further tests are being conducted to determine whether the virus might be harmful to humans.
Officials said a government crisis center has been established to coordinate efforts.
Romania's chief veterinarian, Ion Agafitei, was quoted by Reuters as saying that at least 220 domestic birds have been killed in the area where those cases appeared, and "the process is ongoing and will continue."
The Danube Delta is a major wetland area that serves as a migratory area for wild birds from Russia and other parts of Europe.
Outside of Asia, where it has killed at least 60 people and devastated poultry flocks, according to dpa, the avian-flu virus has so far been confirmed in six regions of Russia and in Kazakhstan.