A downtown Washington water main ruptured early Saturday, shooting a muddy rapid down 17th Street NW, buckling a section of roadway and transforming an excavation site into a massive mid-city lake.

Several pieces of heavy construction equipment, worth millions of dollars, were submerged in the 100-by-200-foot site. A construction official said the water in the hole was at least three stories deep.

“This is a lot of water,” said George S. Hawkins, general manager of the D.C. Water and Sewer Authority.

The 20-inch cast-iron pipe, which runs under the west side of 17th Street, ruptured between M Street and Rhode Island Avenue about 4 a.m. It took several hours for crews to shut off the water by hand-turning valves around the break.

“It’s like trying to stop a river,” Hawkins said.

“There is a tremendous high-pressure flow in a 20-inch line.”

Minor underground flooding was reported at some surrounding buildings, and several were without water for part of the day. Other customers experienced a reduction in water pressure as six downtown waterlines were turned off.

It wasn’t immediately clear what caused the rupture, which Hawkins said will be the subject of “a full forensic study.”

It could have been vibrations from the nearby excavation, he said, or it could have been something else — including age.

The line was installed in 1897, and at 116, it’s about half again as old as the average District water main.

But Hawkins said: “This is not a line that breaks very often, even though it’s old. If we were to predict where a water main break would be in the city, it wouldn’t be here.”

As he spoke, a Hitachi excavator scooped mud out of the hole where the break occurred and dropped it into a dump truck. A street sweeper inched back and forth on a silt-covered section of M Street.

Pumping equipment was unloaded at the water-filled excavation site.

Police blocked several streets around the break site, and water agency workers and contractors raced to restore normal conditions to the neighborhood.

There were valve crews to manage the water flow, crews to analyze the water pipes and crews to clean the storm drains before pumps could remove the many cubic feet of water from the construction hole.

The property, at 1200 17th St. NW, was once home to the National Restaurant Association. That building was demolished, and it is being replaced by an 11-story office building that will be anchored by the law firm Pillsbury Winthrop Shaw Pittman. But first, the site would have to be drained — slowly.

Hawkins said the water main and road repairs would be done before downtown Washington goes back to work Monday. “I never look at a water main break as good fortune,” he said. “But we are fortunate this happened early on a Saturday morning and not Monday.”