A woman has been found dead after fire tore through a house in Sydney's west overnight, police say.

A man is being questioned over the blaze that broke out at the house on Clement Street in Guildford just after 3.30am on Tuesday.

When police and Fire and Rescue NSW officers arrived at the house, they found a man and two children had escaped from the property.

The man is understood to have phoned emergency services to raise the alarm, saying a woman was still trapped inside.

The house was well alight and residents reported hearing a number of explosions, before firefighters extinguished the blaze.

When they entered the property, they found the body of a 30-year-old woman.

The man who escaped from the fire, and who is understood to be aged in his 40s, was taken to Merrylands Police Station where he was being questioned over the circumstances of the blaze.

NSW Ambulance paramedics were later called to the police station to treat the man, who was understood to be suffering from smoke inhalation.

A NSW Police spokeswoman said no further details were available about the circumstances of the fire, or the relationship between the man, woman and children.

A crime scene has been established at the house, and police and fire investigators are expected to remain there throughout Tuesday as the investigation continues.

Inspector Bob McGowan, from Fire and Rescue NSW, praised the efforts of firefighters but said the blaze was extremely difficult to battle.

"We searched the area of the house that we could, but it's a pretty tough situation, when the roof tiles are dropping around you," he said.

"I can't praise [the firefighters] highly enough for the efforts they made to get in there and search."

Anyone with information about the fire has been urged to contact Crime Stoppers on 1800 333 000.