Dublin Fire Brigade says it is likely to take a month before the cause of the fire at the Metro complex in Ballymun can be established.
Chief fire officer Patrick Fleming said there was nothing to indicate that the blaze was suspicious, but it would be several months before the building could be returned to use.
He said the fire in a private residence above the Metro Hotel, which was reported just after 8pm on Wednesday, was one of the biggest blazes that the brigade had dealt with in high-rise buildings in recent times.
Mr Fleming said it was "not a Grenfell Tower-type incident" because there was no issue with the external cladding and the fire spread internally.
The hotel's general manager, Mark Williams, told the Herald that a full investigation had yet to be carried out by gardai and the fire brigade into the cause of the fire.
"We don't think that will be today or tomorrow," Mr Williams said.
"We are working as fast as we can but it will take time."
In a statement released yesterday the hotel apologised, saying: "The Metro Hotel wishes to apologise to hotel patrons and guests that the hotel is currently closed, and will remain closed for some time, following a fire.
"The Metro Hotel is actively engaging with emergency services following the fire which occurred at around 7.30pm on Wednesday evening.
"Unfortunately, guest and tenant access to personal belongings located in the hotel/apartments is restricted until clearance is received from emergency services.
"We will provide regular updates as they become available.
"The cause of the fire is still being investigated.
"No decision can be made about a hotel reopening date until the cause of the fire has been established and all safety considerations have been thoroughly assessed."
Gardai were yesterday telling hotel and apartment residents that nobody could enter the building until a full structural and forensic examination had been carried out by engineers and gardai.
Fire chief Mr Fleming said equipment and resources weren't a problem on the night.
"We had plenty of firefighters and equipment," he said.
"We had two aerial appliances there, which are basically high-rise ladders.
"You can fight a fire like that from the outside or the inside, and we did both.
"Post-Grenfell, we're carrying out a major review of high rises.
"There will be more high rise built in Dublin, it would appear, but there was no issue with equipment.
"We had absolutely no problem with resources or equipment."
Gardai have a statutory function to investigate the blaze, but Dublin Fire Brigade will also look at the fire safety of the building and how the blaze spread, and will be speaking to the owner and consultants working on their behalf.