A 20-year-old man is in custody after four people were found dead inside a house in Markham, Ont.

Police say they were called to the home on Castlemore Avenue in the east end of Markham, about 39 kilometres northeast of Toronto, shortly before 3 p.m. Sunday.

When officers arrived they met a 20-year-old man at the door who was taken into custody, police say.

Police block off a Markham home after four people are found dead. (CTV News Toronto)

Police are not saying who contacted emergency services to notify them of the incident.

“At this point in time the Coroner is here on scene, going through the house, as well as homicide investigators and officers with our Forensic Identification Unit,” York Regional Police Const. Andy Pattenden told reporters from the scene.

Pattendon would not confirm the relationship, if any, between the deceased and the man in custody.

Police said the road would be blocked off to the public for hours. (CTV News Toronto)

The Coroner has been called to the scene. The deceased have not yet been identified and their bodies remain in the home.

Police say they are not looking for any other suspects at this time. 

“The next steps are appealing to the public,” Pattendon said.

“I want to reassure everyone that this is a safe community and we are doing everything we can to make sure whoever is responsible is taken before courts.”

Pascoal D'Souza, who lives across the street and was among those watching officers walk in and out of the home on Sunday, said it was unsettling to see such a heavy police presence in his quiet neighbourhood, where he said the residents typically "keep to themselves."

"It's a shock, because you never think anything like this would happen near where you live," he said.

Anyone with information is being urged to contact York Regional Police or Crime Stoppers.