Jordan Rice, brother Blake and mother Donna were forced to climb on the roof of their car after they were caught in the flood about 2pm on Monday.

The tragic rescue saw a good Samaritan truck driver save Blake, while Donna tried to grab Jordan, 13, after he became separated from the tree the pair was clinging to.

Ms Rice's devastated partner of about 30 years and father to her four children, John Tyson, said Jordan couldn't swim and was terrified of water.

"(The truck driver) went to grab Jordan first, who said, 'Save me brother'. I can only imagine the fear coursing through his body,'' Mr Tyson, 46, said.

"He won't go down with any fanfare or anything like that - I don't think anyone will even wear a black armband for him - but he's just the champion of all champions, a family hero.''

Mr Tyson should have spent last night celebrating his 46th birthday, but was instead at a morgue.

Donna, Jordan and Blake, 10, were just minutes away from picking up eldest child Chris at his house when the car became stuck near the intersection of James and Kitchener Sts in Toowoomba.

The water was only up to the car wheels, but the engine stopped.

Ms Rice could only ring 000 because her mobile phone had run out of credit.

The family was told to stay put and they climbed on to the roof of the car as the floodwaters rose.

Mr Tyson said bystanders looked on until the semi-trailer driver wrapped some rope around himself and jumped in.

The truck driver rescued Blake, 10, first at Jordan's direction.

The rope broke as he went back to get Jordan and Donna, forcing the pair to cling to a tree.

"Jordan was swept off,'' Mr Tyson said.

"As soon as he went, Donna just let go, you know trying to clutch at him. "The poor little bugger, they just both drowned.''

Mr Tyson said he desperately wanted to make contact with the truck driver, who is described as scrawny.

The cement renderer said he would never have let the trio go if he knew there was any sort of risk.

"It really wasn't raining that hard (when they left),'' Mr Tyson said.

"I said to her, 'You be careful in the rain' but not for one instant if I thought there was any sort of risk would I ever have let her go by herself. I wouldn't have even let her go.''

Mr Tyson said his partner of about 30 years was the best mother who loved cooking and gardening.

"I'm great on a shovel, but she done everything else,'' he said.

"I don't even know where I'm going to start.

He described Jordan as a good kid who loved music and drawing.

"He was a very quiet kid,'' Mr Tyson said.

"He was the exact opposite to all the others. He'd wear purple and chrome boots and red skinny jeans and one of those real sad penguin golf shirts.''