Three people were hospitalized after being sickened by carbon monoxide fumes at a home in Gwinnett County early Wednesday, authorities said.

Lt. Eric Eberly, spokesman for the Gwinnett County fire department, said paramedics responded to a call from a house in the 1000 block of Bridal Path Drive in Lawrenceville shortly after 5:30 a.m.

Inside the house, crews found one man with an "obvious medical emergency," Eberly said, and called for additional units.

An engine company with a hazmat unit detected extremely high levels of carbon monoxide, which was coming from a generator in the garage being used to power a heater. The home's electricity had been cut off, Eberly said.

The man and two other people in the house -- an adult female and a teenage male -- were taken to Gwinnett Medical Center for treatment, he said. No firefighters were injured.

The names of the victims were not immediately available, and there was no word on their condition.

The incident comes two months after a similar but fatal incident at a house in Kennesaw.

Michael Cox, 55, and a 21-year-old stepson, James Benjamin Jr., were killed Oct. 20 by fumes from a generator inside the home that also was being used to power a space heater due to the home's electricity being cut off.

Generators are intended to be used outside -- never in a house or enclosed space -- and should be placed far away from the structure, experts say.

Carbon monoxide is particularly dangerous because you can't smell or see it, said Lt. Dan Dupree of the Cobb County fire department. Portable carbon monoxide detectors should be on every floor of a home, much like smoke detectors, he said.

Carbon monoxide concentration is measured in parts per million or ppm, and most detectors will sound an alarm at 70 ppm, Dupree said. A person may experience symptoms such as a headache, dizziness and chest pains at ranges over 100 ppm, according to the U.S. Consumer Product Safety Commission.