Emergency services were called to the house on Greenacre Road, in Greenacre, just after 3am on Saturday following reports of a fire.

Three fire trucks attended the scene, and contained the fire to the "front portion" of the two-storey house, a spokesman for Fire and Rescue NSW said.

Two residents, a 46-year-old man and a 70-year-old woman, were in the property at the time.

FRNSW helped to evacuate the woman, but she suffered minor injuries from the fire, including burns and cuts to her hands and feet.

Graffiti sprayed on the property's fence, front wall, and pavement appeared to say: "U r killer", and "U r murderer".

The motivation for the incident is not known, but police are treating the fire as suspicious.

Several rooms of the house were damaged, but FRNSW said the blaze appeared to have started in a living room or bedroom at the front of the property.

"There is a cloud of suspicion over it," FRNSW spokesman Norm Buckley said.

"Fire investigators are returning to it this morning with a canine. It is a crime scene."

The female resident was treated at the scene by paramedics and taken to hospital.

Police have established a crime scene and have "conducted a canvass of the neighbourhood", but investigations are ongoing.

A detection dog was used to pick up any signs of accelerant, but Bankstown Inspector Matthew West said there were no suspects at such an early stage of the investigation.

"The people are business owners that reside at that location, so we've also got numerous inquiries in relation to their business," he said.

"There's many different directions we need to investigate prior to jumping to any conclusions."

Some neighbours were puzzled by the graffiti.

"It's really strange, because they're really good people," one woman, who asked not to be named, said.

"They keep to themselves, really."

The neighbour said it was scary to be woken to the sounds of fire crews and police in the street.

"It is, especially being woken up to all of that," she said.

"All that matters is no-one got hurt."

Police are appealing for anyone with information to contact Crime Stoppers.

With AAP