The Arts Building and Lecky Library were evacuated after the fire alarm went off at around 14.30pm this afternoon.
Students streamed out of the building stewarded by security staff.
According to a spokesperson for College, the alarm was not a planned drill and the reason the alarm was triggered is being investigated.
The alarm did not affect the Berkeley or Ussher libraries. People have since been allowed to reenter the Arts Building, while no further information about the alarm has been made available.
Earlier today, members of the Postgraduate Workers’ Organisation (PWO) protested outside the Synge lecture theatre, forcing Minister Eamon Ryan to leave through an emergency exit in the back of the hall.