A 13-year-old victim of the devastating floods that swept through the Australian city of Toowoomba earlier this week died after asking his rescuer to save his little brother first.

Jordan Rice and his mother, Donna, were killed on Monday afternoon after being carried off by the floodwaters that had risen around their stranded car.

At least 10 people lost their lives in what police in the Queensland city described as an "inland instant tsunami". Another 18 are feared dead.

Details of the teenager's sacrifice emerged today after his father spoke to the local paper.

John Tyson told the Toowoomba Chronicle that Ms Rice and their sons, Jordan and Blake, were on their way back from a trip to buy school uniform when the waters rose up around their car as they drove through the city's central business district at around 2pm on Monday.

After the engine cut out, Rice, 43, managed to get through to the emergency services, who told the family to stay where they were.

But as the waters grew higher, the three had to climb on to the roof of the car.

"All these people were just standing around until an old scrawny guy grabbed a bit of rope, wrapped it around himself and jumped in," said Tyson.

"Jordan can't swim and is terrified of water. But when the man went to rescue him, he said, 'Save my brother first'."

Although the rescuer managed to save 10-year-old Blake, the rope broke when he tried to tie it around Rice and Jordan, and mother and son were swept downstream.

After holding on to a tree for a little while, the pair were carried off by the floodwaters.

Tyson began to cry as his spoke of the bravery his son had shown in his final moments.

"I can only imagine what was going on inside to give up his life to save his brother, even though he was petrified of water," he told the Chronicle. "He is our little hero."

The father described his partner and Jordan as "the unsung heroes of my life", adding: "She was my soulmate."

Tyson also thanked the man who had risked his own life to help his family and save Blake.

There were also fears today for a Toowoomba-based man who was last seen sitting on the roof of his stranded car with his wife and young son.

Footage shot by a news helicopter showed the man, identified as James Perry, awaiting rescue on Monday afternoon after trying to cross a river near the town of Grantham.

Perry's wife, Jenny, and his son, Ted, were saved by a helicopter, but when it returned, the chopper could not find Perry or his car.

The Queensland premier, Anna Bligh, said that many members of the public had rung her office to ask after the family and say how upset they had been by the footage.

Perry, who is 39, is one of more than 50 people to be declared missing in the region.