Five people died, including an elderly woman lunging for a rescue ladder, after a fire broke out in a 20-story apartment tower in North Bergen, N.J., Sunday afternoon and burned for more than two hours.

The fire started on the fourth floor of the building, which houses mostly elderly people and low-income families, said Lt. Neil D. Sanzari of the North Bergen police.More than 30 residents, some in their 80s and gasping for air, were taken to hospitals. At least seven firefighters were hurt, including one who suffered second-degree burns on the back of his neck and on his ears, the police said.

A few residents fled through the building's garage. Others rushed out the front door, some limping and others using canes. Rescuers carried some residents in wheelchairs down several flights of stairs filled with smoke.

Sanzari said one woman fell to her death as she was about to be rescued.

"She just jumped the gun," he said. "They were bringing the ladder right up to the balcony. But she didn't wait for them to put the ladder on the railing. She grabbed it too quick and pulled it right down."

The other four victims were found in the building and probably died from smoke inhalation, Lieutenant Sanzari said. The authorities had not released the names of the victims by late Sunday night.

The police said the fire was reported at 4:48 p.m. and eventually was upgraded to five alarms.

Fire officials said they did not know the cause of the blaze. But they said several oxygen tanks were found in the apartment where the fire started, and the police said they received many calls from residents and neighbors of the building who said they heard a huge explosion about the time the fire started. Some rescuers speculated that a cigarette could have touched off the oxygen tank.