Group Manager for Greater Manchester Fire and Rescue Service, Andy Heywood said: "At the moment we are applying water to the outside of the building to stop the fire spreading.
"By allowing the fire to burn inside the building it stays hot and gives off smoke which is relatively clean.
"Unfortunately because the building and fire is right next to the railway line we have asked for the trains to be stopped and overhead line equipment isolated.
"It could be several hours before we can be confident of what will happen to the building and how the fire will develop."
More top news
Some of the UK's top horses will be parading through Liverpool from 11am till noon today - perfect timing for half term.
Personalities from across the showbiz spectrum have paid tribute to Pete Burns after the former Dead Or Alive singer died at the age of 57.
The Dead or Alive singer and Eighties icon suffered a massive cardiac arrest on Sunday, his manager and family said.