LAWRENCE, Mass. — A huge blaze started in an empty downtown nightclub early Monday and spread rapidly through 14 buildings, including apartments and a home for the mentally disabled. One injury was reported.

Some people were clad only in pajamas as they fled into the bitterly cold morning, with chills below zero. Water sprayed by firefighters froze, covering buildings and streets with ice.

The flames were spotted by an ambulance crew on an unrelated call, state Fire Marshal Stephen Coan said.

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

Stiff wind quickly pushed the blaze through the block, which included early 1900s three-story, wood-frame buildings.

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

Zulma Borgos, 49, said she was awakened by calls of "Fire! Fire!" from her boyfriend, Elias Riverra. Borgos said that 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 Red Cross shelter set up in a school. Other people arrived in bathrobes and slippers.

The Red Cross said it expected about 35 to 40 people at the shelter. Many of them were already struggling financially, said Bill Meagher, a Red Cross volunteer.

"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."

The temperature was 12 degrees, and the wind made it feel like 2 below zero, the National Weather Service said.

One person was injured in the fire in Lawrence, about 30 miles north of Boston, Fire Chief Peter Takvorian said. The extent of the person's injuries was unknown.