St. Louis, MO- One person is dead and another seriously injured from carbon monoxide poisoning in St. Louis.

Firefighters arrived at a four-apartment complex Friday to find a person unconscious and another feeling sick. The St. Louis Post-Dispatch reports officials found high levels of carbon monoxide inside the building.

The cause of the carbon monoxide leak is under investigation. The names of the victims were not immediately made available.

Other occupants of the building declined treatment.

Laclede Gas. Co. responded to the building to determine whether the leak was caused by a natural gas-related malfunction.