Two apartment buildings in Southwest Roanoke County were evacuated early Sunday after firefighters detected high levels of carbon monoxide, a spokeswoman for the fire and rescue department said.

A resident at Villages at Garst Creek called 911 after she was awakened by her carbon monoxide detector just before 3 a.m., spokeswoman Jennifer Conley Sexton said.

Firefighters found high levels of the odorless, colorless gas in her apartment and 10 others, Conley Sexton said. Firefighters evacuated about 15 people from those apartments.

Emergency personnel treated one person with oxygen, Conley Sexton said. That person did not want to be taken to a hospital.

Fire officials determined that carbon monoxide was leaking from two gas-fed water heaters, and that the heating, ventilation and air conditioning system was distributing the gas to the apartments in the two buildings.

Residents were allowed to return to their apartments after the gas had been turned off and their apartments ventilated.

Fire officials praised the woman for having a working carbon monoxide detector.

"This may have been a tragedy," Deputy Fire Marshal Brian Simmons said.

-- Amanda Codispoti