The rupture to the 12-inch water main was reported about 9 p.m. yesterday on the mauka side of the highway between Bethel and Bishop streets.

The break sent thousands of gallons of water gushing onto the highway, forcing the closure of lanes in both directions. Work crews spent most of the night clearing debris and by mid-morning today had dug a 20-foot-long trench that was 18 feet deep and 14 feet wide.

"It's very large," said Wanda Yamane, a spokeswoman for the Honolulu Board of Water Supply. "There is a crack along the main and they are trying to find out where the crack ends."

The break occurred under the right lane of Nimitz fronting the Topa Financial Center, formerly the Amfac building. A river of water covered all four lanes, including portions of two that had lifted and sank.

Police detoured westbound motorists to Alakea Street and blocked Queen Street heading to Nimitz.

This morning, only the two ewabound mauka lanes of Nimitz Highway remained closed. When repairs are finished, the water board plans to repave the highway, Yamane said.

It was not known what caused the break. Glenn Ah Yat, Honolulu Board of Water Supply lead pipe fitter, said the pipe's age may have contributed to the break.

No one could say for sure last night how many residents and businesses were affected. Crews had to shut off water in the area to identify the source of the gushing water. Service was restored early this morning, Yamane said.

Brian Grayling, who manages the 360-unit Harbor Square, said his nearly 2,000 tenants had no water last night.

"I've been managing high-rises for over 20 years and this is one of the worst cases I've seen. It just affects a very concentrated population," Grayling said. "If we have a fire, there's no water to put it out."

Gregory Rawlings, who lives on the top floor at Harbor Square, took the lack of water in stride. "We've already declared it a day off tomorrow. Since we can't take a bath we're just going to stay at home," Rawlings said. "We have about one gallon of water for spare, so it's going to be a short bath."