The woman pulled from the Toowoomba flash floods on Monday had sought refuge on top of a car.
But less than a minute after she clambered on to it, the vehicle - which was wedged on top of another car - was washed away.
Madsen, 49, a photographer for Toowoomba newspaper the Chronicle saw the drama from the second level of the carpark at a nearby shopping centre.
About 15 minutes later, Madsen left the carpark and 120 metres away found Andrew Sharp, from the nearby town of Crows Nest, clinging to a tree with flood waters rushing over him. Mr Sharp was also washed away, but plucked to safety.
The sudden rainfall turned a small creek - one of two in the city - into a rapidly rising torrent within minutes.
The floodwaters were so strong they swept away cars and other debris including a large water tank which destroyed a pedestrian bridge as it floated down the street.
Madsen said he had covered fires and other disasters, but the floods were the most severe incident he had photographed in his 22-year news career.
"Just a very surreal day," he said. "It was hard to believe it was happening. It's a bit bizarre.
"We're up on the top of a range 700 metres up so flooding's usually just fairly minor."
The waters disappeared almost as fast as they arrived, leaving debris strewn throughout the downtown area and cars piled atop one another.
Madsen said the women shown in his photograph had probably been walking in the street when what was described as an "inland tsunami" of floodwaters overwhelmed them.
Madsen was standing with others at the shopping centre.
"There were people hanging over the railing, just watching."
He had not seen how quickly the waters rose, as that had happened by the time he arrived.
"It was very quick," he said. "It was a matter of minutes, I think, that the first wall came through."
In video film also shot by Madsen, police and rescue staff can be seen standing in thigh-deep water as they talk on cellphones and work to rescue others.
Cars are carried off by the heavy river flow and the water tank is seen crashing into the pedestrian bridge.
Rescuers from the Queensland Fire and Rescue Service, who have been trained for swift water recovery, work with ropes to haul people to safety.
In Brisbane, roads became jammed by central city workers fleeing home as river levels rose.
The state's premier, Anna Bligh, warned the worst lay ahead. A high tide tomorrow was threatening to push flood levels above the 1974 record.
"Now is not a time for panic, now is the time for us to stick together," she said.