Belfast City Hall has been illuminated in the Belgian colours following terror attacks in Brussels which killed 31 people.
Earlier a book of condolence was opened for the victims.
At least 31 were killed and more than 200 injured after explosions at Brussels Airport and a city centre metro station.
Two bombs exploded at Zaventem airport just after 7am on Tuesday.
Around an hour later a bomb was set off at Maalbeek Metro.
Isis, which was behind the Paris attacks, also claimed responsibility for the Brussels bombings.
Belgium is in the midst of three days of mourning, and government offices, schools and residents held a moment of silence on Wednesday morning to honour the dead.