Search teams plodded through mud-laden riverbanks and flew aircraft over the flood-stricken landscape of central Texas for a fourth day on Monday, looking for dozens of people still missing from a disaster that has claimed at least 78 lives.

The bulk of the death toll from Friday's flash floods was concentrated in the riverfront Texas Hill Country town of Kerrville, accounting for 68 of the dead, including 28 children, according to Kerr County Sheriff Larry Leitha.

The Guadalupe River, transformed by predawn torrential downpours into a raging, killer torrent in less than hour, runs directly through Kerrville.