A 12-year-old boy has died after high levels of carbon monoxide were detected at an Airdrie apartment complex on Sunday.

Airdrie RCMP said in a news conference late Sunday that police initially responded to a medical distress call, and once they arrived on scene they realized high levels of carbon monoxide were present.

The apartment complex — in the 700 block of Willow Brook Road in the northwest part of the city, just north of Calgary — was then evacuated.

Evacuees were taken to Genesis Place recreation centre.

"The building has been evacuated to either an adjacent building in the same area or onto available transit buses," said EMS spokesman Stuart Brideaux.

The four-storey building has 136 units and resources were called in to help the affected residents.

At 3:40 p.m., Airdrie Fire Department allowed all residents except those from six units to return to their homes. RCMP said the six units are part of their ongoing investigation.

The boy passed away in hospital at approximately 5 p.m.

Police said two of the child's adult family members also were taken to hospital for treatment.

One additional patient was treated at Genesis Place.

"Our hearts and thoughts are in the family of this young boy," said Insp. Kim Pasloske.

"In deference of the grieving family, we will not be releasing his name."

"The community of Airdrie is very close, and this news hits us very hard," she added.

Officials said they've determined the cause of the carbon monoxide leak and finished ventilating the building.

"We had extremely high readings of 2,100 parts per million on the second floor, which is really quite elevated," said Airdrie Fire Department deputy Chief Garth Rabel.

Pasloske said police are in the early stages of their investigation into the incident.

Symptoms of carbon monoxide exposure include headaches and feeling nauseous or tired.

"Just generally unwell, headaches are very common," Brideaux said.

"As the exposure begins to rise, however, people may become unconscious or unresponsive and if left untreated, ultimately, high levels of carbon monoxide can be fatal."

The fire department requested that residents, upon returning home, open their window a crack, turn on the bathroom fan and leave the bathroom door open for one to one-and-a-half hours to allow air to circulate and clear the remaining traces of carbon monoxide.

RCMP also reiterated the importance of having carbon monoxide detectors in homes and workplaces.