About 20 people were evacuated from two units following a fire at Cessnock late last night.
Police and fire officials will examine the cause later this morning.
Four people were taken to hospital following the Dixon Street fire in two units.
Superintendent Adam Dewberry from Fire and rescue NSW says more than 20 fire fighters found the blaze.
About 21 people were evacuated from the intense blaze.
The fire is being treated as suspicious.