Dramatic footage has captured the moment a motorway collapsed during heavy rain in the northwest Italian city of Genoa on Tuesday killing at least 25 people.
Vehicles and debris fell 45m on to the railway tracks, buildings and a river as rescue teams scrambled to find survivors.
One witness described the sound of the bridge collapsing like "thunder".
"We heard an incredible roar and first we thought it was thunder very close by," an unnamed witness told the BBC.
"We live about 5km from the bridge but we heard a crazy bang... We were very scared... Traffic went completely haywire and the city was paralysed."
Eyewitness Davide Ricci told local newspaper Secolo XiX that he thought he saw lightning strike the bridge moments before it crumbled.
"The debris from the collapsed (bridge) fell 20 meters from my car," Ricci said, according to CNN. "The central pylon crumbled, then the rest came down."
Engineers claim it is too early to determine the cause of the collapse.
Giogio Larosa posted a photo and video on Instagram of rescue workers scrambling to clear the debris away in heavy rain to find survivors.
He also posted an image from the bridge at the point the bridge collapsed.
Around 200 metres of the 45 metre-high bridge came crashing to the ground in large blocks - along with the cars and lorries travelling on it.
"We're not giving up hope, we've already saved a dozen people from under the rubble," said rescue official Emanuele Giffi.
"We're going to work round the clock until the last victim is secured."
At least 25 people have already been found dead and the search for survivors continues among three areas where the debris fell.
"Unfortunately there are around 30 dead and many injured in a serious condition," Interior Minister Matteo Salvini told reporters.
"There are buildings that have been hit but it seems that all the victim were on the bridge," Giffi said.
Thanks to a public holiday on Wednesday, the industrial zone spanning the area below the highway was almost empty when Tuesday's disaster struck.
'Complete chaos'
Not far from the scene, onlookers climbed to the roof of a shopping centre to watch the procession of helicopters arrive and depart throughout the search.
"I live nearby and I cross the bridge every day on foot," said Ibou Toure, 23, a translator. "I was never sure of it, you'd always hear these noises whenever lorries were going over.
"When I heard it had collapsed, I wasn't surprised."
Inside the search area, rescuers are busy with dogs, evacuating bodies on orange stretchers.
Nearby, around 15 people, some with blankets wrapped around them and crying, look on at the wreckage.
Rescuers on the bridge. Source: AAP
The heavy rains which greeted relief workers to begin with later gave way to better weather but the air is filled with the smell of sewage.
Patrick Villardry, a firefighter from Nice in France specialising in search and rescue missions, waited nearby with two dogs, Arco and Missile.
The pair previously helped recover a woman from an earthquake in L'Aquila, central Italy, in 2009.
"For now the Italian rescuers have told us to wait. There is complete chaos at the moment, they told us."
A highway bridge has partially collapsed near Genoa Italy. Source: IPA Milestone
But dogs used on relief missions often tire quickly, he explained, and Arco and Missile will be called up.
"For now, the first surface victims have been evacuated," he said.
"Now they have to search under the rubble of buildings and there are thousands of tons of concrete."
