Police are investigating whether a wild street brawl is related to a house fire that killed a teenager in south-west Sydney.

Fire crews and police responded to the blaze which ripped through a two-storey brick home on Montana Way in Macquarie Fields just after 1.30am on Wednesday.

A woman and her five children were able to escape the flames after smoke alarms woke them, but police said it “became apparent” a 14-year-old visitor was not accounted for.

Fire and Rescue Deputy Commissioner Jeremy Fewtrell said the intensity of the heat and smoke of the fire meant crews were unable to rescue the teenage boy.

“When they arrived they found a very well-developed fire, a very intense fire,” Commissioner Fewtrell said.

“Crews reported flames of about two metres [high] coming out of all the windows,” he said.

“Despite their best efforts, they just couldn’t enter the building due to the intensity of the fire at that time.”

After the fire was extinguished, crews found a body in an upstairs bedroom.

A few hours earlier at 10.30pm on Tuesday, police were called to a brawl on the same street.

“The police were called [after] reports of people fighting,” Superintendent Julian Griffiths said.

“That scene was cleared by the officers

“It has been made aware to investigators and will be encompassed within the scope of the investigation.”

The blaze started early on Wednesday morning. Photo: ABC

Superintendent Griffiths said he couldn’t answer whether anyone from the house was involved in the street fight but police were “still looking into that line of inquiry”.

“The fire is undetermined, so all aspects of the fire and the causal factors are being reviewed as part of the investigation.”

Police said they were unable to confirm whether the occupants of the house knew the teenage boy was staying the night or if he snuck into the house.

Deputy Commissioner Fewtrell said it would have been very difficult for the 14-year-old to get out of the house.

“We know that heat rises [and] clearly being upstairs in that premises would’ve been very unpleasant and very difficult to escape from,” he said.

Superintendent Griffiths said it was a “tragic situation”.

“It’s a really tough day, obviously a devastating day for the family involved but also our crews who have that heartache to work through as well,” said Deputy Commissioner Fewtrell.

Anyone with information about the incident, or who has dashcam vision about the time the fire broke out, is urged to call Crime Stoppers on 1800 333 000.

-ABC