Four people found dead in a Markham, Ont., residence on Sunday afternoon were killed, York Regional Police have confirmed as a man arrested at the scene is set for a court appearance Monday.

Const. Andy Pattenden told CBC Toronto that the man, 20, is in custody and will appear in court "at some point today."

Pattenden also said the identities of the four would not be released until after post-mortems.

Suspect was inside when police arrived

Police were called to a residence on Sunday shortly before 3 p.m. ET, near Castlemore Avenue and Mingay Avenue, after receiving a report that multiple people had possibly been injured.

Officers made contact with a man at the front door and he was taken into custody. The man has not been charged.

After searching the residence, officers found four bodies, police said Sunday evening in a news release.

A coroner and homicide detectives have been called to the scene in Markham, a Greater Toronto Area city about 30 kilometres northeast of downtown Toronto.

Const. Andy Pattenden said police are appealing to members of the community for any information they may have regarding the homicide case. (Richard Agecoutay/CBC)

Investigators are appealing to anyone with information to contact police.

People living near the crime scene have expressed shock such an incident could happen in their neighbourhood.

"I've lived here since 2002 and it's been a quiet neighbourhood. You know everyone on the street," Pascoal D'Souza told CBC Toronto.

Members of the community gathered Sunday night near the Markham home where four bodies were found. (Richard Agecoutay/CBC)

He said that when police cruisers started to arrive, he thought it might be a robbery.

"Never did I think it would be what I heard right now."