A Sydney man who saved his flatmates from a fire at a Condell Park townhouse in the city's west has told 9NEWS he knows who the arsonist is.

Scott Wagemaker says he was woken by the sound of broken glass at about 3am, and when he went downstairs he found his lounge on fire.

"I saw the bloke there and he had something in his hand and he threw it on top of the flames," he said.

Scott Wagemaker was left with nothing more than his undies after the fire broke out at the Condell Park property. (9NEWS)

Mr Wagemaker says he knows the man who started a fire in his home earlier this morning. (9NEWS)

Wearing only his undies, Mr Wakemaker brandished a garden hose to tackle the blaze. (9NEWS)

"I've got two gas bottles inside the house, they're huge.

"I was just yelling fire, fire, fire."

The 47-year-old, wearing only his blue underpants, ran to get a hose while yelling to alert his housemates.

They managed to jump from windows, remarkably escaping with only minor injuries.

Fire crews managed to extinguish the blaze at the home in Sydney's west. (9NEWS)

Fire crews managed to get undies man a shirt. (9NEWS)

Mr Wagemaker returned to the gutted home on Mitchell Street this afternoon, and broke down as he told 9NEWS about losing valuable possessions.

"What upsets me the most is my mother's ashes are still there...they've been melted too," he said.

He also said that the person he believes was behind the attack could be one of his former housemates.

"Hand yourself into police, because they're coming after you," he said.

A witness told 9NEWS they believe a molotov cocktail sparked the fire.

The man located in the home has not been further described, however a dark-coloured hatchback was seen driving from nearby Leemon Street, shortly after the fire.

Investigators have appealed to the public for information about any unusual or suspicious activity in the area overnight.