Parts of the Glasgow School of Art Mackintosh building are to be dismantled after it was ravaged by fire earlier this month.
Glasgow City Council said surveys had revealed substantial movement in the building's walls and that a sudden collapse of parts of it was likely.
Work to partially dismantle sections of the building is expected to begin as a "matter of urgency".
The building, which was completed in 1909, was gutted by fire on 15 June.
The city council said remote surveys and close-in surveys from baskets suspended from cranes above the charred remains of the structure had revealed more substantial movement in its walls than previously thought.
They have concluded that a sudden collapse of parts of the building was likely, rather than possible.
The statement said: "There is now a requirement to at least partially dismantle sections of the building as a matter of urgency.
"However, the dangerous nature of the site - which includes the Mackintosh building and the O2 ABC - is such that it will take around two days to devise a methodology for taking down the south facade, which is the most seriously affected part of the building.
"The west gable of the Mackintosh building has continued to deteriorate and the east gable has continued to move outwards.
"It is not possible at this time to say exactly when the work will begin, but it will be as soon as possible."
The council has also warned about the risk of falling bricks or stonework on Sauchiehall Street.
Raymond Barlow, the authority's head of building control, said: "With each passing day, a sudden collapse becomes more likely.
"It has become urgent that we take down the south facade. As the process begins, it will be likely that the other walls will also need to be reduced.
"We do not know what effect this will have on the rest of the building, so I have to be clear this site remains dangerous and is becoming more dangerous.
"It is particularly important that people observe the cordon which remains in place."
The fire was the second blaze in four years at the Charles Rennie Mackintosh building.
It was still undergoing renovations from the 2014 fire when it was engulfed by flames. The renovated Mackintosh library had been due to reopen next year.
In a statement, Glasgow School of Art acknowledged that damage to the building was "significantly greater than had initially been anticipated".
However, it said the aim of the work would be to achieve structural stability.
The statement said: "The areas of significant concern are the east elevation, the west elevation and sections of the south elevation.
"The plan of works will involve [site contractor] Reigart undertaking extensive down-takings and potential structural bracing.
"Due to the condition of the Mackintosh building, this work will be undertaken in a highly-controlled way to minimise any potential risk of failure and be sufficient to achieve structural stability of the Mackintosh building."
'Unable to return'
Meanwhile, the first minister has said that residents and businesses affected by the fire will receive compensation.
Nicola Sturgeon said a hardship and relief fund would be made available to those who had been displaced.
Traders on Sauchiehall Street have warned that the fire could spell the end for some businesses, while some residents living within the exclusion zone around the site have been unable to return home since 15 June.
Speaking during First Minister's Questions, Nicola Sturgeon said: "The Scottish government will make £1,500 available to each household, which will be match-funded by the council to make a total of £3,000 for each household.
"In addition, we will confirm increases in support for affected businesses, increasing the amount that the Scottish government contributes towards business rates from 75% to 95%."