The centre of Madrid's business district has suffered widespread disruption after a fire gutted a 32-storey building.
Some upper levels have already collapsed into floors below
About half a million commuters have faced disruption as roads and train services in the area remain shut down.
The city mayor has issued a government order to ensure businesses near the burned-out shell of the Windsor building remain shut.
The authorities say there is a high risk that the building could collapse.
"At first they told us we'd be evacuated from our homes but then they said we were far enough to be safe," one male resident told the BBC.
"But we're frightened of the building collapsing. It's an uncertain situation that changes from minute to minute."
Some of the restrictions imposed on transport routes in the area were lifted on Monday.
The fire, which left seven people injured, started on Saturday but was only brought under control on Sunday.
The top floors of the landmark building have already fallen into lower storeys, reducing the skyscraper to a smoking, blackened skeleton.
Madrid's mayor, Alberto Ruiz-Gallardon, said the situation remained critical and offices in the area would remain closed until at least Wednesday.
He said the fire was believed to have been caused by a short-circuit on the 21st floor.
The mayor said the demolition of the building was inevitable and investigations were under way to see how it could be carried out safely.
He told a news conference that firefighters would be able to enter the building on Wednesday - 48 hours after the blaze was finally extinguished.
Monica Reyzabal, the daughter of the building's owner, told Spanish news agency Efe the demolition would take about six months as it would have to be carried out "little by little" to prevent damage to adjacent buildings.
Nearby is the prestigious El Corte Ingles store.
The security company Prosegur, whose security guards were in the building when the blaze started on Saturday, said its employees acted with "absolute diligence" well beyond the call of duty.
As one guard called the fire brigade, others tried to put out the blaze using fire extinguishers "despite thick black smoke".
Prosegur told the BBC its security guards ordered the evacuation of the building and checked all the floors to make sure no one was left inside.
As the blaze continued on Sunday, large pieces of the Windsor building plunged to the ground as the blaze destroyed its top floors, sending columns of black smoke into the night.
Nearby bars, nightclubs and blocks of flats were evacuated as flames ripped through the building, one of the capital's most emblematic structures.
Madrid fire chief Javier Sanz told local radio the 106m (350ft) tall building was still unstable.
"It is clear the structure has been damaged and has suffered high temperatures, and we cannot be certain that a pillar, girder or some other structural element will not collapse," he said.
Prime Minister Jose Luis Rodriguez Zapatero visited the scene on Sunday.