Multiple family members in Kentucky were reportedly discovered unconscious in a garage Wednesday morning, two of whom later died.

“We’re calling this a death investigation. It appears to be a horrific accident,” Louisville Metro Police Department Lt. Emily McKinley told WAVE. “Again, this is just a reminder, in the cold months to be cautious of running vehicles inside of closed, indoor areas, specifically garages.”

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“Just be aware of the risks of carbon monoxide poisoning. This is what this appears to be at this time,” McKinley continued.

Two young children – a 3-year-old boy and a 7-year-old girl – were discovered within a vehicle and their father was located in the garage when officers got to the scene in the neighborhood of Valley Station, the police lieutenant told the outlet.

The father and 3-year-old died following the incident, while the older child was listed as being in critical condition, the outlet reported.

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“The car was inside the garage. The children appeared to be inside the car. And the male was outside of the car,” McKinley said. “It appeared to be that he had warmed the car up while it was sitting in the garage and then tried to get the kids out the door for school and start the day.”

The incident came to light after neither the father nor his daughter appeared at work or school, respectively, WAVE reported.