Complex sentence: Hundreds of firefighters and 45 fire engines were involved in efforts to control the fire, and later attempted to control pockets of fire on the higher floors after most of the rest of the building had been gutted.
Split into simpler sentences: Hundreds of firefighters and 45 fire engines were involved in efforts to control the fire. Firefighters were trying to control pockets of fire on the higher floors after most of the rest of the building had been gutted.