NY, NY – An explosion rocked a Queens home yesterday afternoon and badly burned one of its residents as firefighters and utility crews were searching for the source of a natural gas leak wafting through the neighborhood.

Two hundred neighbors were evacuated as police officers and firefighters cordoned off a block on 41st Street in Sunnyside, near 48th Avenue, and shut down the gas and electricity as a safety measure. Con Ed crews eventually found and began repairing the broken gas main that fire officials said caused the leak.

The explosion disrupted family preparations on the eve of the Thanksgiving holiday, as residents returning from work were barred from their homes.

The victim, Kunta Oza, 69, was taken to the burn center at NewYork-Presbyterian Hospital/Weill Cornell Medical Center in Manhattan. She was in critical condition last night with severe burns over much of her body, fire officials said. As worried relatives gathered at the hospital, her son, Joe Oza, said, he had no information about her prognosis.

One other occupant of the building was treated at the scene for minor injuries.

City Councilman Eric N. Gioia said he spoke with Mr. Oza and received the following account: Mr. Oza’s wife, Clara, had called him from the house, at 48-19 41st Street, about 3:30 p.m. complaining of a gas odor. Concerned, she left with their two children. But Mr. Oza’s mother and a housekeeper remained.

Many neighbors said that after they had smelled gas about 3 p.m., firefighters came and searched the area, but then left. Then Con Ed crews arrived, and a company spokesman said the utility called the Fire Department to return.

Shortly after the firefighters returned, residents reported hearing a boom at about 4:30 that reverberated through the neighborhood.

A neighbor who lives around the corner, Francis Cianfrocca, 47, described it as “a short, sharp explosion.”

Councilman Gioia questioned why the firefighters initially left. “That’s the question that’s on my mind,” he said. “That’s on everybody’s mind.”

A fire chief at the scene, Ed Kilduff, said that the firefighters believed that the gas leak was under the street, and that they had not found a strong odor of gas in homes. When Con Ed crews arrived, they said that they could handle the situation, so the firefighters left, the chief said. But then the Con Ed crews had trouble gaining access to the basements of homes and asked the firefighters to return and help, which they did, the chief said.

A Con Ed spokesman agreed with that account, but he said that the utility’s problem was not getting access to basements but rather to manholes that were obstructed by parked cars.

Further investigation determined that a six-inch-diameter gas main pipe under the street had broken, and that the leaking gas migrated along electrical conduits into 8 or 10 homes on the block of two- and three-story Tudor-style attached houses, Chief Kilduff and Con Ed said. The chief said that he could not confirm or deny speculation that the explosion was ignited when Mrs. Oza turned on a light switch in the basement.

It was unknown what caused the break in the gas main. Fire officials said that they did not consider the leak suspicious.

How long the main had been broken was also unknown, but the landlord of a nearby building, Frank Szabo, said his tenants reported smelling gas two or three days earlier. A Con Ed spokesman, Alfonso Quiroz, said that the utility was cooperating with the Fire Department in a joint investigation.

At a temporary shelter set up by the Red Cross in nearby Public School 199, Gladys Valette, who lives two doors away from the explosion, recalled her own reaction to the blast. “Oh, my God, we need to get out!” she said as she grabbed her son, Kerwin, 7, and ran out of the house.

Now she is contemplating spending Thanksgiving at the shelter. “Maybe tomorrow we need to get turkey in the street,” Mrs. Valette said. But fire officials and Con Ed said they were working to return most of the families to their homes later in the night, and some residents were being escorted across the barricades around 11 p.m.

Though neighbors said they saw no flames at the site of the explosion, Chief Kilduff said that there was fire damage to that house, but no danger of collapse. The adjoining homes were not affected.

One resident, Francisco Herrera, said that he had just finished showering when the explosion hit. He was so startled that “I ran out into the street in a T-shirt and my underwear,” he said. He went back inside to get sweat pants before being evacuated from the house.