The number of deaths after what a state police official called a "devastating tornado" hit Greenfield and the surrounding area was not clear. Another person died in nearby Adams County.
Electric utility CenterPoint Energy estimated 80% of its affected customers would have power restored by Sunday evening as the region faces another warm day.
Nearly 550,000 homes and businesses remained without electricity in Texas early Saturday as the National Weather Service warned of temperatures soaring to around 90 degrees.
In addition to flooding, severe thunderstorms are forecast for many of the same locations under flood watches, including cities like Dallas, Houston and Lake Charles, Louisiana.