A key road bridge over the Mississippi river in the US state of Minnesota has collapsed in the evening rush hour killing at least seven people.
At least 60 were injured when part of the I-35W bridge in Minneapolis gave way at 1805 (2305 GMT) on Wednesday.
As the structure buckled, up to 50 vehicles were hurled into the water.
The US Department of Homeland Security said there was no reason to suspect the collapse of the bridge, which had been undergoing repairs, was terror-related.
"Obviously this is a catastrophe of historic proportions," Minnesota Governor Tim Pawlenty told a news conference.
Fire chief Jim Clack said rescuers did not expect to find any more survivors after the search was called off earlier because of darkness.
"At this point we have seven confirmed fatalities, and we expect that number to go up," he said.
The 40-year-old bridge was last inspected in 2006 and no significant structural problems were found, Mr Pawlenty added.
Russ Knocke, a spokesman for the Department of Homeland Security, told AFP news agency: "There are no indications of a nexus to terrorism at this time."
Traffic had been "bumper to bumper" at the time of the incident as only one lane was open in either direction on the eight-lane road because of the construction work on the arched bridge.
Tons of concrete crashed 64 feet (20 metres) into the water as the structure crumbled.
A freight train passing underneath was crushed as a 500ft (150m) span of steel and concrete collapsed.
Injured people waited for rescue as vehicles dangled off the crumpled concrete and smoke billowed into the sky from the fiery wreckage of a lorry.
Some managed to swim to safety.
"The bridge started falling, cars were flying everywhere and I saw the water coming up," Catherine Yankelevich, whose car ended up in the water, told AFP news agency.
"The water was coming up pretty fast, so I rolled the window down... It seemed like a movie, and it was pretty scary."
Eight-lane, steel-arch bridge
Built in 1967
Used by 140,000 cars a day
Some 60 children were led to safety with only minor injuries from a school bus that clung to the side of a collapsed section over the river.
Divers and rescue boats scoured the water for survivors, but the operation had to be called off as night fell because darkness made it too dangerous to search the water among mangled steel and submerged cars.
Minneapolis police chief Tim Dolan said officials had accounted for all but one of the construction workers who had been on the bridge at the time of the collapse.
Eyewitnesses said they heard a huge roar as the structure fell into the river.
"What I first heard was a giant rumbling sound from my apartment," Mark Lacroix told the BBC.
"I'm 20 storeys up, just a stone's throw from the bridge itself, and I thought, maybe my own building was coming down, it was an amazing noise. And I look out of the window and I see just the final moments of it collapsing into the river.
"It really took quite a while for me to realise that this was not a planned explosion... to realise it was a tragedy."