Video report by ITV News Correspondent Stacey Foster
Residents were told to immediately evacuate after the fence-like barrier along the historic Shropshire town’s Wharfage shifted overnight and there was further movement on Wednesday afternoon.
West Mercia Police Chief Superintendent Tom Harding said the flood defences had been "compromised" and were "buckling" in some areas in a video post on Twitter.
Residents reported hearing a loud bang when the barrier was shunted into a kerbstone by the fast-flowing River Severn and water seeped under the barrier.
Stacey Foster on "worrying times" in Ironbridge as the integrity of the flood defences remain under doubt
Mark Sitton-Kent, director of operations for the Environment Agency said: "That movement of it backwards caused it to clatter against the kerbstones behind with a loud bang that I think everybody heard.
"That alarmed residents and caused a multi-agency response.
"There was a fear that there would be some collapse of the barrier, which it hasn't done and is not likely to do."
A severe 'danger to life' flood warning remained in place for the River Severn at the Wharfage, Ironbridge.
Flooding along parts of the river, which remained close to its highest levels in some areas, is likely until at least Sunday, the Environment Agency said.
Police could be seen knocking on doors along the riverside to ensure that residents living on Wharfage had left their homes.
But some residents declined to leave their properties, including one occupant who also opted not to move a car parked within yards of the riverside.
War veteran Albert Darlington, a resident of Ironbridge, told ITV News he is not worried about the flooding as it stands as he is "watching the situation" from his home.
He said he's only concerned if the flood barriers break, in which case the water will "come down in a rush and that's a different matter."
Mr Darlington added: "But at the moment it's only slopping over the top and coming underneath, so you only get a dribble down this end."
His home did flood in 2000, when there were no barriers in place, but he said he does not feel in danger.
"Even if the water does come down... you'll have a foot of water on the floor, there's still no need to panic," Mr Darlington said.
"You only panic if you get Niagra Falls and you're underwater and you can't do nothing. It'll take hours to get up to like that, it would have to come under all the doors and you have got an hour or so to get out."
Speaking at the scene, Mr Sitton-Kent, said the barrier had been undermined by the sheer volume of water.
But the agency said it did not believe the barrier was under threat of an outright breach.
Councillor Shaun Davies urged people not to come to Ironbridge as it was a "developing situation".
Mr Sitton-Kent said: "Over the next 24/48 hours as the river level here drops, we will move in and do some work to shore up the area and make sure it stays put.
"We are also pumping out the water that is seeping under and coming through."
Homes in Bewdley on the Shropshire border were also evacuated after the river spilled over barriers at Beales Corner.
The Environment Agency forecasts the river level in the town, which has risen more than two metres in the past 72 hours, from 3.36m to 5.45m, will peak at 5.48m on Wednesday and remain at a near-record high into Thursday.
It reached its highest level of 5.56m on November 2, 2000.
Marc Lidderth, environment manager for the Environment Agency, said: "Over the next 24 hours, we will see the river levels remain elevated at Ironbridge and further upstream at Shrewsbury.
"Further downstream into Bridgnorth and Bewdley, the peak is making its way down the system.
"We will be seeing the peak at Bewdley happening round about later this afternoon.
"Unfortunately we have already seen some of our barriers over-topped there in the early hours, where properties have flooded."
Geoff Baker is one of those whose home in Bewdley was flooded after water breached the flood defences.
The 88-year-old said he was "upset" that he had not had "enough warning" to move items out of the way of the flood water.
Shrewsbury Railway Station remained closed on Wednesday morning after flood waters hit the Severn Viaduct - the main route in for the majority of lines.
Network Rail described the flooding as a "once in a generation event".