Gas-powered generators emitting dangerous fumes have sent more than 20 people to area hospitals suffering from carbon monoxide poisoning.

Only one death has been reported since the storm hit Thursday. But hospitals are on heightened alert for those coming in with headaches, nausea and dizziness ¬­— symptoms of inhaling the odorless, colorless and highly toxic gas.

Yesterday, a family of four was taken to Anna Jaques Hospital in Newburyport; two were taken to Caritas Holy Family in Methuen, and two more were taken to Saints Medical Center in Lowell. All were treated and released.

Lowell General Hospital would only say they had fewer than five cases but all were admitted. They were listed in stable condition. At Saint Joseph's Hospital in Lowell, seven people came in with symptoms; four were treated and released and three were admitted but expected to be home soon.

On Friday, six people were taken to New Hampshire hospitals with carbon monoxide poisoning, treated and released. A Danville, N.H. man — identified yesterday as 49-year-old Larry Jenkins — died of carbon monoxide poisoning from the generator he was using in his camper after his power went out Thursday night. Also found in the trailer was Jenkins' dog, which is expected to survive.

"We tend to be a little more vigilant (about looking for carbon monoxide poisoning symptoms) when people have been tied up in their homes with generators going," said Dr. Domenic Martinello of Anna Jaques Hospital, since a person may not be aware of its presence in their home until they start to develop symptoms.

Carbon monoxide is a colorless and odorless gas that is very toxic, blocking red blood cells from moving oxygen through the body.

Martinello said there is a sliding scale of symptoms of carbon monoxide poisoning, starting with headaches, nausea, vomiting, and confusion that can escalate to coma or death. The faster the person is treated, the less the chance of long-term effects, he said.

"It's a time-sensitive thing," Martinello said, adding that long-term effects can include seizures, memory impairment, and other neurological problems, as well as an increased risk of heart attack and other cardiac problems.

Martinello said the treatment is simple — oxygen. More serious exposure may require treatment in a hyperbaric chamber, which is filled with oxygen pressurized higher than the atmosphere.

Martinello said if you suspect carbon monoxide poison, call 911 immediately. Also shut off the generator, open windows to ventilate the house or just get outside.

The U.S. Consumer Product Safety Commission warns users to to keep running generators outside the home and garage, as well as away from windows and vents. When used inside, the generator can fill a home with carbon monoxide within minutes and it will linger for hours.

Merrimack Valley Hospital in Haverhill had no reports of carbon monoxide poisoning.

Parkland Medical Center in Derry and Lawrence General Hospital did not return calls last night seeking information on any carbon monoxide poisoning cases there.

Staff writer Terry Date contributed to this report.