Police hunting killer of Sydney teen

Police are hunting the man who fatally shot a 15-year-old boy as he lay in bed at his family's southwest Sydney home.

The man kicked in the door of the family's Glenfield home at 6am on Friday, then shot the boy in the head, in what is suspected to be a revenge attack.

The teen, who cannot be named for legal reasons, was rushed to The Children's Hospital at Westmead in a critical condition but died just hours later.

The shooting is reportedly connected to another homicide, with the victim known to police.

Police are now searching for the man responsible for the killing, who has been described as being 18 to 20 years old with a thin build.

He was last seen wearing grey tracksuit pants, a navy blue hooded jacket and white joggers and may still be armed.

"We need to speak to a number of witnesses, we don't know who the offender is," Detective Chief Inspector Mark Brett said.

"It's going to be a long, drawn out process."