Authorities have confirmed the presence of carbon monoxide inside a parked Ford Explorer in Toldedo, Ohio, in which five people were found unresponsive. Three of them died on Wednesday. 

The incident is being described as an accident. The driver had pulled the vehicle into a parking lot after it got a flat tire. The victims were discovered Wednesday morning, the Associated Press reported. 

The victims included a grandmother and her grandchildren. The woman's son had discovered the bodies and called for help, according to City of Toledo spokesperson Rachel Hart. Two children were hospitalized in critical condition. 

Investigators placed a meter inside the vehicle and started the engine with the doors closed, Toledo Fire Chief Allison Armstrong said. The meter showed a "high spike of carbon monoxide." 

The investigation into what caused the gas to accumulate inside the vehicle continues.