Firefighters are committed to staying at the scene of the Sauchiehall Street fire for “as long as it takes”.
The fire, which started in Victoria’s nightclub, continues to smoulder.
There are fears around the structural integrity of the building where the blaze started.
Police remain at the scene of the fire working with the Scottish Fire and Rescue Service (SFRS) and have warned the building is still “difficult to access”.
Several road closures and diversions remain in place until further notice.
A police spokeswoman said: “A joint investigation is ongoing to establish the cause of the fire. However, it is not believed to be suspicious at this time.
“The building remains difficult to access due to damage. We continue to work with partners with regards to those businesses in the area which are affected. Please continue to follow the relevant social media accounts in order to receive updates.”
The SFRS said a lot of work was still to be done to make sure the fire on Sauchiehall Street is completely extinguished.
About 30 firefighters and eight fire engines remain in attendance at the site and firefighting is “ongoing”.
More than 120 firefighters tackled the incident at the height of the blaze, which was compared to fighting a “blowtorch”.
SFRS officials also confirmed there is no risk to the public from asbestos after concerns were raised during the height of the blaze on Thursday.
Assistant Chief Officer Lewis Ramsay said: “There is still a lot of work to be done on the ground to ensure that this fire is completely extinguished.
“We will remain on the scene for as long as it takes and we are absolutely committed to preventing any further damage to surrounding properties and ensuring the area is made safe.”
The SFRS say the blaze took hold in several commercial properties including a nightclub, causing extensive damage to a four-storey block.
Firefighters have been at the site since fire broke out just before 8:20am on Thursday.
Mr Ramsay added: “This was an incredibly difficult and complex incident - but the actions of our firefighters were and continue to be outstanding.
“This is a historic area of Glasgow - through our aggressive intervention and planning we were able to protect iconic buildings, such as the Pavilion Theatre, from significant damage.
“I would like to take this opportunity to thank the hotels, businesses and people of Glasgow who opened their doors to our firefighters and our emergency service partners for their invaluable and continued support.”
Glasgow police warned a number of road closures will remain in place today.
In statement the force said: “A joint investigation is ongoing to establish the cause of the fire, however, it is not believed to be suspicious at this time. The building remains difficult to access due to damage.”
At the height of the blaze, an asbestos warning was issued to local residents and businesses as firefighters battled the blaze, which was brought under control on Thursday afternoon.
Fire chiefs say atmospheric testing has concluded “there is no risk to the public” from asbestos.
Chief Fire Officer Alasdair Hay added: “It’s one of the biggest incidents we’ve had in the Scottish Fire and Rescue Service since its inception.”
No-one was injured in the incident.
Shows at the Pavilion and nearby Theatre Royal were cancelled in the wake of the incident.
The Pavilion thanked emergency services for saving the “grand old lady” of Renfield Street.
A statement posted on the Pavilion Theatre Facebook page on Thursday evening said: “We managed to gain access tonight to ascertain the damage within the theatre.
“As the building across the lane is still currently pouring out smoke, this is still coming into the theatre.
“There is still a lot of smoke within the auditorium and the seats, plasterwork, carpets and curtains are covered in a layer of black ash. We cannot see that we will be able to reopen within the next few days.”