BT said some internet users may have been affected on Wednesday as a result of the fire at one of its buildings in central Belfast.
The blaze on the fourth floor of Telephone House, May Street, was reported just before 6am but was extinguished by fire crews after six appliances and an aerial ladder attended the scene.
The PSNI website was unavailable as a result of the fire.
Also on Wednesday morning both Translink and the Police Ombudsman’s Office told their Twitter followers that their websites were not working.
A BT spokeswoman said she did not know “the geographical location of the customers affected or the numbers involved at this stage”.
She added: “The fire has affected our customers in the data centre and there are repercussions because of that.”
“Investigations as to the cause of the incident are currently under way,” a BT spokesman added.
The NIFRS said the fire is being treated as “accidental”.