There are fears this morning that part of a set of units at Charlestown may collapse after a fire tore through the structure.
Emergency services rushed to Fraser Parade at about 4am to reports a blaze had ignited in a two-storey residential building.
It took 40 firefighters to stop the flames spreading through the entire block and the fire was only extinguished after an intense two hour battle.
Fire & Rescue NSW says at least one of the units inside the building has sustained significant damage with a risk the roof and walls could collapse.
Paramedics have reported no injuries so far, but until the structural integrity of the charred unit can be shored up, FRNSW investigators are unable to enter the space to confirm no one was inside.
Fire & Rescue NSW Superintendent Adam Dewberry said work to secure the unit and give firefighters access inside would likely take the best part of Saturday.
Investigations into the cause of the blaze will also have to wait until then.