Raymond Barlow, from the council’s building standards team, told the BBC the building had been “fatally compromised” and the remaining structure was “highly dangerous”.
He pointed out that one of the most dangerous elements left behind was the floating chimney stack, which would be the first part to be brought down.
Barlow also said it was not possible for the council to say exactly which aspects of the building could be saved, nor how long the demolition will take.
He said: “You are talking a good number of weeks before we see any change to aspects around here.
“We need to start work at one end of the site, take off the highest bits of danger and hopefully that will let us start to access parts of the station and get the station back up before coming to the façade.”
The council said crews would work around the clock, but timescales were weather-dependent as cranes cannot be used in high winds.