A 12-inch water main break early yesterday on Kapi'olani Boulevard snarled traffic on the thoroughfare for much of the day.

The main broke at about 12:10 a.m., between Kamake'e Street and Ward Avenue, forcing officials to shut down Kapi'olani Boulevard while the work was under way. The main was repaired by about 11 a.m., and crews re-opened the roadway by about 4 p.m.

It's unclear what caused the main to break, but officials said it is old and is being replaced as part of a water and sewer rehabilitation project along Kapi'olani Boulevard.