Police are warning drivers to dig out their tailpipes before starting their cars, after at least two people — one of them an 11-year-old boy — appear to have died from carbon monoxide poisoning today, while two other children were hospitalized.

“Most people have never seen this much snow,” Boston police spokeswoman Cheryl Fiandaca said.

The 11-year-old victim was digging out a car with his father on Nazing Street off Blue Hill Avenue about 11:30 a.m. when he got in the passenger side to warm up. He died at Boston Medical Center around midday, authorities said.

A second victim, described as a male in his 20s, was found in a car on Woolson Street in Mattapan about 4:20 p.m. In East Boston, two children, ages 5 and 8, were pulled from a car and hospitalized with carbon monoxide poisoning, police said.

Neighbors of the 11-year-old desperately tried to revive the boy, whose father suffered a heart attack at the scene.

“The first thing he said when he came through was, ‘Where is my son?’ and he just started crying,” said Sheila Adams, who was riding out the storm at her daughter’s home nearby when she heard someone screaming to call an ambulance.

Her daughter, Shakiena Phifer performed CPR on the boy and is devastated by his death

“She is still beyond upset right now,” Adams said. “The neighbors came together as a whole to do what they could do until help arrived.”

The second fatality, described as a male in his 20s, was found about 4:20 p.m. on Woolson Street.

As the tragic news broke, state Fire Marshal Stephen Coan made a desperate plea to people digging out from this weekend’s blizzard to make ventilation of their homes, businesses and cars their first priority.

Coan said many modern houses have wall-mounted outside vents for their furnaces, which must be cleared on the outside or the fumes from the heater will build up inside their home.

“Many houses are built with these kinds of vents that are 2 to 4 feet above the ground,” he said. “With 5- to 7-foot drifts, they’re covering them up.”

Coan also warned people that barbecue grills and generators should only be used outside with plenty of ventilation to avoid fumes in the home that can poison people who live there.

“History is a good teacher here, after any kind of storm, whether it’s a hurricane, snow storm or tornado, as the storm wears down you’ve got to get people to pay attention to carbon monoxide,” he said.

Coan also cautioned people warming up their cars as they dig them out of high snow piles or running them to charge cell phones, should first clear their tail pipes to allow engine exhaust to vent into the air, otherwise it can find its way into the car’s cabin.

“You’ve got to have ventilation (for exhaust) if you’re going to dig your car out. Clear out the exhaust vent first,” Coan said.

He also urged people all over the area affected by the storm to dig out fire hydrants near their homes.

“If there’s a fire in your neighborhood we don’t want to waste precious time looking for a fire hydrant,” Coan. “I say, ‘Adopt a fire hydrant.’ “