Neighbours of a woman found dead after a house fire in Wollongong heard two people laughing and speeding off in a car as flames engulfed the home.

Emergency services were called to a fire at the two-storey house in Doncaster Street, Corrimal, about 2.30am today.

Fire crews extinguished the blaze and found the 31-year-old woman's body inside. She is yet to be formally identified, but the Illawarra Mercury reports she was believed to be a Wollongong lawyer.

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Fire and Rescue NSW Superintendent Ian Krimmer said it was not known what started the fire nor what caused the woman's death.

He said the house was "extensively damaged".

A neighbour, who did not want to be identified, said she heard noises about 2am.

"I thought I heard smashing on the floor, so my husband got up to turn some lights on.

"I heard a man and a woman walking past our place and they went to a car and slammed two car doors.

"This couple ... were laughing while this house was ablaze and I thought it was a strange thing to be getting in your car and laughing.

"They just took off straight down the road."

People in the street gathered outside the burning house after calling emergency services and saw smoke billowing from the windows as firefighters battled the blaze.

The neighbour said they noticed the woman's front door was open, but the screen door was closed.

"[Another neighbour] said the deceased had been worried about a prowler for a couple of days," she said.

Wollongong Local Area Command duty officer, acting Inspector Daniel Richardson, said police were investigating several leads, including the reports of the couple speeding away.

"We've got some differing versions of events," acting Inspector Richardson said.

"[Neighbours] saw a couple of males nearby smoking cigarettes, but that was up the street."

Acting Inspector Richardson said an arson dog had been taken through the house, but the results of that search were not yet known.

Police do not know yet whether the fire was suspicious, he said.

Firefighters also battled five other blazes around Sydney overnight.

Seven people were evacuated from a home in Macquarie Fields and 13 people were evacuated from a unit block in Granville.

Superintendent Krimmer said a mother and two children were treated for smoke inhalation after a fire at their Wentworthville home just after midnight.

There were also fires at an unoccupied house in Emerton and a house in Quakers Hill.