Police have located the family of a boy who was found walking the streets of Fairfield this morning.

Police said the boy, who is believed to be three or four years old, was found knocking on doors in Fairfield's Regent Street about 4.15am on Sunday morning.

Although he could speak to police officers, they were unable to identify him.

The boy was described as being of Pacific Islander appearance, about one metre tall, with a solid build and long black hair.

He was wearing only a blue sloppy joe and a nappy when found. The child was originally described by police as a girl.

"We have no idea who [he] is or where [he's] come from, but [he] could have snuck out of the home while [his] parents were asleep during the night," Fairfield Police Inspector Robert Adam told ABC radio.

AAP