Four young children were discovered unconscious in their home in Xanthi, a city in Northern Greece on Friday morning, likely due to a suspected gas leak.

According to local reports from xanthinews.gr, the children’s mother went to wake them for school and found them unresponsive. She immediately alerted the police and fire department. Emergency responders entered the home in protected suits and transported the children to the hospital in Xanthi.

The children, three girls aged 3, 5, and 7, and a 9-year-old boy, are reported to be in serious condition. Authorities revealed that the basement, where the children’s bedrooms are located, had an environment that appeared suffocating due to poor ventilation and potential gas accumulation.

Moreover, the incident comes a day after work was carried out on the property to install a liquefied petroleum gas (LPG) tank. Investigators are examining whether the installation is connected to the suspected gas leak.