Police closed several blocks in the North Side neighborhood and the Chicago Transit Authority briefly shut down a nearby train station and rerouted buses.
A hole in the street quickly grew to 25 feet long and the torrent ripped a light pole and several parking meters from the sidewalk.
"It was a dramatic scene," said Tom LaPorte, spokesman for the city's Department of Water Management. "That's lot of water to come out of the pipe all at once. The deepest was about 4 feet of water."
It was not clear what caused the 80-year-old, cast-iron main to break at about 1:30 a.m., but LaPorte said weather could be a factor.
"It went from very cold over the weekend to warmer temperatures that can cause weakness in the pipe," he said. Temperatures at the time of the break were in the teens.
Traffic was light at the time of the break in the area of homes and small businesses, but the water partially submerged some parked vehicles.
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