A heartbroken dad has told how his two daughters aged 13 and 11, have both tragically died after beingswept away in devastating floods and his parents are both missing.

Rescuers are continuing to scour a devastated central Texas landscape of mangled trees, overturned cars and muck-filled debris in an increasingly bleak mission to locate survivors, including 27 girls who have not been seen sinceCamp Mystic was slammed with a wall of waterin a storm.

And RJ Harber has said that his daughters Blair, 13, and Brooke Harber, 11, both have died in flooding in Kerr County but were not at Camp Mystic.

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Paying tribute to the pair he toldCNNthat Blair “was a gifted student and had a generous kind heart,” while Brooke “was like a light in any room, people gravitated to her and she made them laugh and enjoy the moment.”

Mr Harber also told the TV network that his parents Charlene and Mike were missing and he believes they have died.

The two girls were pupils at St. Rita Catholic Community where Blair was preparing to enter eighth grade and Brooke was about to start in sixth grade, confirmed the school. The school held a prayer service on Saturday afternoon to grieve and honour their lives.

They were understood to have been staying with their grandparents by the Guadalupe River and their parents were unharmed having been in a separate cabin.

"Please keep the Harber family in your prayers during this time of profound grief. May our faith, our love, and our St. Rita community be a source of strength and comfort in the days ahead," said Fr. Joshua J. Whitfield, pastor, in correspondence with church members, reported CBS News.

The flooding in Kerr County has killed at least 43 people, including 15 children, and eight people are confirmed to have died in nearby counties.

Authorities still have not said how many people were missing beyond the children from Camp Mystic, a Christian summer camp along a river in Kerr County where most of the dead were recovered.

The destructive, fast-moving waters rose 26 feet (8 metres) on the Guadalupe River in just 45 minutes before daybreak on Friday, washing away homes and vehicles. The danger was not over as rains continued pounding communities outside San Antonio on Saturday and flash flood warnings and watches remained in effect.

Searchers used helicopters, boats and drones to look for victims and to rescue people stranded in trees and from camps isolated by washed-out roads.

Gov. Greg Abbott vowed that authorities will work around the clock and said new areas were being searched as the water receded. He declared Sunday a day of prayer for the state.