An underground water line ruptured early Saturday in downtown St. Paul, flooding several city blocks and temporarily causing a widespread drop in water pressure, officials said.

Rick Larkin, the city's director of emergency management, said there was "significant street damage" after the 20-inch main broke around 12:30 a.m., sending thousands of gallons of icy water rushing through eight to 10 square blocks. It wasn't immediately clear what caused the leak, Larkin said.

The line ruptured between on Wall St., between 5th and 6th Streets, near the Farmer's Market.

A few hours later, officials isolated the break and closed the valves to turn off that portion of the water supply. Full water pressure was restored to most of the grid, but Larkin said public works crews will have to dig up a large section of road to repair the broken part of the line.

The area where the leak occurred is full of apartment and office buildings. Larkin said it didn't appear there was much structural damage beyond the streets themselves.

"It's a hilly area of the city, so it all just ran down the hill," he said.

With water pressure dropping for much of the area overnight, some hospitals switched temporarily to reserve water supplies.

Officials closed several downtown streets after the break, but Larkin said crews were working to reopen many of them before dawn. Part of the work involved clearing away the ice from the ruptured line that had made it to street level.

"Once the street is cleaned up and the ice dealt with, it'll shrink back to a one-block area," Larkin said. "... It really becomes a construction project."

By 9:30 a.m., workers were pumping water out of hole where the leak occurred. Roads were wet, but the application of salt kept them free of ice.