BENEATH this bridge, submerged in the muddy water, could lie the most heartbreaking story of the Queensland floods. What was once a railway overpass crossed daily by freight trains is now, resigned rescuers fear, a marker for a mass underwater grave.

Bobbing in the murky, debris-strewn water below the Grantham bridge are up to 30 crumpled cars, violently wedged against the pylons after being washed downstream in the ferocious flash flood that hit the country town on Monday.

But it is the likely contents of those mangled vehicles that has police and emergency workers filled with dread.

"You'd have to think with 30-odd cars here, we're about to find some pretty unpleasant things," a police officer at the scene said yesterday.

Within the once 300-strong community of Grantham there are at least 50 people missing. So far, just three have been confirmed dead. Communication is a struggle, with no power or phone lines. Everyone is resigned to the fact that there will be more dead - and that some will be found under the bridge at Grantham.

The consensus among survivors and rescuers alike is, if you haven't been found by now, you simply couldn't have survived.

Images from the disaster at Grantham

As a team of specialist disaster divers arrived by RAAF Black Hawk helicopter yesterday and began entering the swollen river, locals took a breath and prepared for the worst.

"I know there is a body in that white car ... it's a mother my husband couldn't get to," a resident, Karen, said. "He got her daughter off the roof but he couldn't get to the mum."

Karen said she heard a young girl, aged about 15, screaming for help and saw her clinging to the roof of the car amid a ferocious torrent of water.

"My husband ripped the door off the car. He tried to help the woman - but he couldn't," she said.

Another local, Martin Warburton, also knows there are bodies caught beneath the bridge. He saw them there himself, caught in the water.

"I thought they were people swimming, then I realised they were dead," he said. "You saw hands, legs, hair being thrashed about. By the time I got close to the water, I realised they weren't swimming, they were gone."

The specialist police team wasted no time wading into the water to begin their grim search yesterday.

Dressed in wetsuits, divers waded out to the first upturned car.

On the riverbank, an officer was collected registration plates to use in the identification process of the bodies they expected to find. As each vehicle was located, it was pulled from the water by a bulldozer and towed on to dry land and searched.

"The divers out there are basically looking for people in the cars, then we bring the vehicles in here and have a good look for anything else that might be of interest to us," an officer said.

From the nearby railway tracks, locals watch on in hope, but also fear.

Children have been kept away from the bridge and told to remain at the local primary school, which was set up by authorities as an evacuation site.

"You know what: At this stage I just want to know who is alive and who isn't," resident Ken Dutton said.

The recovery mission continued until dusk, and starts again at first light today. A Defence source said military helicopters had not lifted any bodies out of the flood zone by late yesterday. But the source said the grim task was likely to begin today using Black Hawk and Sea King helicopters based at the Amberley RAAF base, just west of Ipswich.

The once-vibrant community of Grantham has become a ghost town, likened by some to the Victorian village of Marysville, which all but vanished in the 2009 Black Saturday bushfires. A quick look is all it takes to see why such a comparison has been made. In Grantham, just a single street of houses remains intact - the homes built on high ground.

Everything else has been flattened.

"I've lived here for 58 years and this place is unrecognisable. It is like a war zone," Gerald Kundle said.

Originally published as Fear this bridge is a mass grave