There are reports that up to 50 Irish people may be missing in the rubble of the World Trade Centre.
The figure was previously thought to have been about 20.
The Department of Foreign Affairs said that about 50 Irish people are still unaccounted for.
A spokesman said the department did not know if the 50 were missing in the rubble or merely out of touch with their families, who have received no report of them since the attacks on the WTC.
Many of the missing are known to have been travelling in other parts of the US when the attacks took place.
The figure is in addition to the five Irish people who have already been confirmed dead.
The original list of missing Irish drawn up by the Department of Foreign Affairs included about 2,500 names - but this has now been whittled down to 50.