The death of a three-year-old boy in a townhouse north of Brisbane is still unexplained, with police regarding it as suspicious until proven otherwise.

Two people of interest could help explain the mystery death of a toddler in a townhouse north of Brisbane.

The three-year-old boy was found at the Kallangur complex early on the morning of June 18.

He was pronounced dead at the scene after apparently falling down a set of stairs, with his family in the building at the time.

Detective Acting Senior Sergeant Gregory Millmore said police had spoken to the family and everyone who was present at the time, but declined to say what the family had told police.

“I’d say we have two main persons of interest with respect to this matter. Obviously we tend to treat all deaths that are unexplained as suspicious until we can prove otherwise,” he told AAP.

Police on Friday urged anyone living in the building on Goodfellows Rd or visiting it the day before to come forward.

“The investigation’s quite well advanced, but we’ve got reason to put out a public appeal,” he said.

“We have reason to believe that people could have information that we’re not aware of.

“We’re particularly chasing any person who has not already brought information to police.”

Detectives spoke to a number of people in the days after the death but have yet to receive a final post-mortem report.