Eight Dublin Fire Brigade units have concluded a search of the old tax office on Chancery Street after a blaze at the building this morning.
It was believed children may have been hiding in the office block.
A fire brigade spokesman said three children were seen exiting the vacant building after the alarm was raised at 8.15am.
The children leaving the building told emergency services there were more children inside the building.
Members of the fire brigade carried out a search using breathing apparatus and declared the building clear shortly after 11am .
The spokesman said three fires had broken out on the ground floor of the six-storey former tax office. Fire fighters extinguished the fires, he added.
He said the blaze was most likely caused by vandalism, adding that squatters were probably residing in the derelict building.
The Red Line Luas which passes in front of the former tax office is running as normal.
Chancery Place, which was closed this morning, has reopened to traffic.
