A massive seven-alarm blaze that started in an empty downtown nightclub quickly spread through 16 buildings Monday, destroying homes and businesses and forcing residents to flee in their pajamas into bitter cold.

One person suffered minor injuries in the blaze at Market and South Union streets that engulfed apartment buildings and a home for the mentally disabled.

The fire was first spotted by an ambulance crew on an unrelated call about 2:30 a.m., state Fire Marshal Stephen Coan said.

Coan said the fire started in the nightclub, which was being renovated. The club had no walls, and that "gave the fire an opportunity to take hold very quickly," he said.

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Freezing winds quickly pushed the blaze through the block, which included early 1900s triple-decker wood frames. Firefighters were hampered by wind chills that dropped to 2 below zero, freezing the water used to fight the blaze and covering buildings and streets in ice.

Zulma Borgos, 49, said she was awakened by calls of "Fire! Fire!" from her boyfriend, Elias Riverra. Borgos said when she looked out the window, "I couldn't believe what I saw."

"It was a ball of fire," said Riverra, 21. He didn't even have time to grab a pair of socks before waking Borgos' three girls in the apartment and running.

The girls, ages 5 to 12, were wrapped in blankets when they arrived at a shelter the Red Cross set up in a local school. Other people arrived in bathrobes and slippers.

Police Lt. Scott McNamara said about 150 people were evacuated from the area. By Monday afternoon, 54 were at the Red Cross shelter, he said.

Bill Meagher, a Red Cross volunteer, said many of those displaced by the fire already were struggling financially.

"A lot of these people who were burned out today don't have anything," he said. "They're not going to be able to find housing right away.

"With the freezing cold weather ... all the shelters are full," Meagher said.

Fire officials said the cause was suspicious. Coan said state and city fire officials were investigating the blaze with the Bureau of Alcohol, Tobacco, Firearms and Explosives.