Updated

A man is in custody on suspicion of intentionally starting a fatal five-alarm fire Thursday in a New York City apartment building as part of a domestic dispute with his child's mother, authorities said.

Charges are pending against the unidentified 45-year-old suspect, who lived in the now fire-gutted five-story building at 41 Spring St. in the fashionable Soho district of Manhattan, according to police spokesman Paul Browne.

Witnesses saw the suspect start the fire in a second floor hallway at about 6:40 p.m. after a domestic dispute with the woman, Browne said. He said the woman and the child are accounted for.

One person was killed in the fire. Browne said the unidentified victim was apparently not part of the dispute and was found on the third floor fire escape burned beyond recognition.

An off-duty firefighter from Los Angeles, who was dining in the area, spotted the flames and ran over to the building where he was confronted by the suspect who wouldn't let him into the building, Browne said.

The suspect also fought with a police officer and New York City firefighters who were trying to enter the building. The suspect was treated at a hospital for bruises and a police officer was treated for a broken hand, Browne said.

About 200 firefighters responded to the blaze, which quickly spread to the upper floors and through the roof, according to FDNY Chief of Operations James Esposito.

Esposito said firefighters had to use the rear fire escape and portable ladders because the heavy fire had burned away the stairways.

"We had an extraordinary amount of fire," said Esposito. "The fire encompassed all the walls and all the floors."

Esposito said the fire completely gutted the inside of the building and at least nine people, including seven firefighters, suffered minor injuries. It was declared under control at 9:20 p.m.

"It's essentially destroyed and it's not going to be livable for quite some time," Esposito said of the building.

A neighbor who lives two buildings down from the fire, Juliet Gentile, 35, said she was home and smelled smoke. She said she went up to her roof and saw the flames.

"As soon as I saw that I got to get out of here," said Gentile. "It was coming right out. The whole thing was in flames."

The American Red Cross said their disasters responders were at the scene to provide emergency housing, blankets, mental health support and other forms of assistance.

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Associated Press writers Tom McElroy and Tom Hays contributed to this report.