A new cull of 4,000 cattle is under way in the North following confirmation of the second foot-and-mouth outbreak there.
The mass slaughter would also extend to smaller numbers of pigs and sheep in the area around the latest case in Ardboe in Co Tyrone.
The development comes six weeks after the North's only other outbreak at Meigh in south Armagh.
It also comes less than two weeks after EU export restrictions had been lifted for most of Northern Ireland.
The North's Agriculture Minister Ms Bríd Rodgers has confirmed an emergency meeting of the Northern Ireland Executive would be held on Monday and officials from various departments would gather today to draw up an agreed strategy on how to move forward now.
"It goes without saying that this is a huge setback for the whole of Northern Ireland agriculture industry and comes just at a time when our hopes were high that we might have escaped this dreadful scourge," she told a news conference at her department headquarters in Dundonald in East Belfast today.
First tests on 22 animals owned by farmer Mr Paddy Donnelly earlier in the week came back negative for foot-and-mouth but subsequent results confirmed it.
Shge said it was the first instance of a contradiction between early and later laboratory exam results.
Ms Rodgers added: "I have to say at this point that further tests are being carried out as a matter of urgency to provide further conformation that we are really dealing with foot-and-mouth disease, especially in view of the original test results.
"However, I would be reluctant to hold out any real hope that this is a false alarm."
PA