Honolulu officials told residents in an emergency message to leave the area downstream of Wahiawa Dam, because it's failing or expected to soon fail. The warning told residents to carpool because of heavy traffic.

Thousands of residents in towns north of Honolulu were told to evacuate their homes early Friday morning as flooding from heavy rains intensified and water levels rose behind a 120-year-old dam.

An evacuation order was issued early Friday morning local time for Haleiwa and Waialua, including areas near the Wahiawa Dam, according to Oahu Emergency Management, which warned that the dam "may col...