A father who was supposed to be helping his 11-year-old daughter celebrate her birthday will soon face a first-degree murder charge in her death, police said Friday.

Peel regional police Const. Danny Marttini said an undisclosed injury to 41-year-old Roopesh Rajkumar has delayed the formal laying of the charge in the death of his daughter Riya, but she said it was expected later in the day.

The girl's body was found in Rajkumar's home shortly after an Amber Alert was issued alerting the public to the child's disappearance. The girl's mother had gone to police after Rajkumar allegedly failed to return the girl on time after taking her out for her birthday.

"It's very heart-wrenching," Marttini said, noting that both mother and daughter shared a birthday. "We have to remember that this is a family, and she's now moving forward without her daughter. It's very traumatic."

Riya's mother sounded the alarm on her daughter's disappearance after receiving information that Rajkumar allegedly intended to harm himself and the child, police said. Marttini said officers began an investigation right away.

Rajkumar, who did not live with his daughter, has been described as her mother's former boyfriend.

Marttini declined to share many details of the investigation, including the cause of Riya's death or her father's injuries.

She said Rajkumar was taken to a trauma centre for treatment but remains in police custody.

Tributes have poured in for Riya since police announced her death early on Friday morning.

Flags at Meadowvale Village Public School, where the girl was a Grade Five student, were at half-mast as students offered tributes and struggled to come to terms with what happened.

"Riya was a well-liked student, and her death is deeply felt by everyone at the school," Principal Stacy Service said in a statement. "Even students who did not personally know Riya will also be affected."

Near the home where the girl's body was found, neighbours offered prayers and left floral bouquets in tribute.

Emmanuel Okafor, who lives nearby, paused near the home, clasped his hands and said a silent prayer.

"I pray to God the family lives through this," he said. "No family should ever go through this ... It breaks my heart."

Okafor said he followed the situation closely after the Amber Alert was issued.

"It's senseless," he said. "We were really hoping last night she would be found alive, not knowing this morning we'd have this tragic news."

Christopher Willis, who also lives nearby, said the neighbourhood was stunned by the news.

"It's shocking to know this could happen close to home," he said, adding the story has particular resonance for him as the father of a three-year-old girl. "It just seems impossible."

Jennifer Fuller, who has a daughter around the same age as Riya, laid flowers a snowbank near the home.

"It's sickening and it's sad," she said.

Marttini said Rajkumar would likely make a court appearance in the coming days.