Emergency services were called to an apartment at a Devonshire Street complex in Surry Hills about 3.30am today after a fire broke out on the second floor.
Three people were outside the unit trying to put out the flames when firefighters arrived to extinguish the blaze before it could spread to surrounding units, police said.
The trio were treated at the scene by paramedics for serious burns and taken to different hospitals, where they currently remain.
Acting Superintendent Gretchen Atkins said police believe the fire was deliberately lit but are unsure how it was started.
“At this point in time, we believe the fire was deliberately lit,” she said.
“We’re really seeking information, appealing to witnesses, anyone who was in the area for CCTV or dashcam footage.”
Crime scene investigators are still combing through the unit as investigations remain ongoing.
