Crews were called to a ground-floor flat on Dryden Close in Worsley Mesnes at around 4am today.
They could see smoke pouring from the building as they arrived and broke down the door to get to the fire.
It is thought that people squatting in the flat had set fire to clothes in the kitchen.
There was no-one inside when firefighters arrived and they worked to put out the blaze.
While there was smoke in communal areas, other flats were not affected and residents did not need to be evacuated.
But the flat where the fire started was damaged by the fire and covered in soot.
Gareth Gray, watch manager at Wigan fire station, said: “There was quite a bit of damage to the kitchen.
“It was probably people sleeping rough who set fire to something and made their way out.
“There were a few needles which meant we had to be careful.”
The flat has now been boarded up to stop other people getting inside.