Police have said no crime has been committed and they believe no other person was involved in the incident at Belfast's Christmas market on Wednesday evening.
A man is fighting for his life after he was found with stab wounds at the gates of city hall.
Stunned visitors told of their fear that they had been caught up in a terrorist incident after the recent lorry attack on a crowd at a Berlin Christmas Market that killed 12 people.
Onlookers said there was panic as families were evacuated from the market.
The man, aged in his 40s, was treated at the scene by an emergency ambulance crew before he was rushed to the Royal Victoria Hospital.
Belfast Health Trust described the man's condition as critical.
On Thursday morning police said no crime had been committed.
Detective Inspector Rowland said: “Whilst we are at the early stages of the investigation, police do not believe at this time that any other person has been involved in this incident”.
The market is to open as usual on Thursday.