Police are probing the “unusual” deaths of four people found by a relative at a home in Melbourne’s north, with another theory emerging.

Detective Inspector Dean Thomas said police were called to the Broadmeadows home following the “unpleasant” find about 2am on Tuesday.

On arrival, they found the bodies of three males, aged 37, 32 and 17 and a 42-year-old woman.

The uncle of the teenager made the grim discovery when he peered through the window and saw the 17-year-old boy lying on the floor.

The man, named by media as Corey, said he suspected drugs could be involved.

But police are exploring all possibilities, including a second theory that has emerged — carbon monoxide poisoning.

Police said it was not immediately obvious what had caused the four deaths.

“It may be from a drug overdose, it may not,” said Thomas.

“It’s unusual that we find four people deceased in the one property potentially from a drug overdose but we’ve got to keep an open mind until we can confirm that’s the case.”

The bodies were found in the same area of the house, leading police to believe they were sitting together.

There was no evidence to suggest there had been any violence inside the home.

Police believe one of the victims lived at the home and three others were visiting.

Their bodies are yet to be formally identified.

The Broadmeadows house is taped off as police investigate. Photo: AAP

The Daily Mail identified the teen victim as Abdul El Sayed, 17, who had an 18-month old child.

His mother, Jessica Lewis, reportedly visited the scene of the tragedy and broke down in tears on Tuesday.

A number of distressed people, believed to be friends and family, could be seen hugging one another in disbelief outside the property, which was taped off by police.

One man tried to enter the scene, but was stopped by officers.

Devastated relatives were later escorted inside the home by police.

Forensics investigators wore full hazmat suits and carried oxygen tanks as they inspected the site.

Thomas said police didn’t believe the deaths were suspicious and a report would be prepared for the coroner.

A number of distressed people visited the scene of the tragedy. Photo: AAP

Corey Lewis, who discovered the bodies, said he first went to the home and knocked on the door but no one answered.

He says he looked through a window and saw a 17-year-old boy lying on the floor.

“I’ve come home to find family members in the house deceased and it just tortured me, shocked me,” he told Nine’s Today program.

“I think (it was) an overdose but I’m not too sure exactly.”

-with AAP