GENOA, Italy -- At least 35 people died after a section of a highway bridge in northern Italy partially collapsed Tuesday, the office of the Governor of the northwestern Liguria region said on its official Twitter account, citing unnamed sources from the fire department.
A further 13 people were injured, five severely, according to Angelo Borrelli, head of the Italian Civil Protection Agency.
Speaking to journalists Tuesday afternoon, Borrelli said that around 30 vehicles and several heavy-duty trucks were on the affected section of the Morandi Bridge, which lies to the west of the port city of Genoa, when it gave way.
The number of casualties is expected to grow as the rubble is removed, Borrelli said, but it is unlikely that anyone was underneath the bridge at the time of the collapse, he added.
According to police, violent storms were partly to blame for the disaster. Maintenance work was also underway at the time to consolidate parts of the bridge, according to motorway operator Autostrade. A bridge crane had been installed to allow the work to be carried out, the operator said in a statement.
"The works and the status of the viaduct were subject to constant observation and supervision," the statement said. "The causes for the collapse will be the object of an in-depth analysis a soon as it will be possible to safely access the site."
'It was frightening'
The incident at the bridge, a concrete structure opened in 1968, occurred around noon (6 a.m. ET) Tuesday, Italian state police said.
The A10, which runs across the bridge, is a major highway for residents and tourists in Genoa, connecting the city with the nearby airport, and a key route along the Mediterranean, linking the Italian coast with French coastal cities to the west.
The disaster occurred during peak tourist season -- when many French tourists would have been using the highway -- and one day before a national public holiday when many Italians travel to coastal areas.
Davide Di Giorgio was filming the heavy rain from the window of his office in Genoa when he saw part of the bridge crash to the ground.
"As soon as I turned the camera on to record the rain, we heard a loud noise and the bridge collapsed," Di Giorgio told CNN. "It took me three seconds to realize what happened."
"My colleagues and I were shaking. It was frightening," he added.
Eyewitness Davide Ricci told local newspaper Il Secolo XIX that he thought he saw lightning hit the bridge shortly before it crumbled. Flashes of lightning can also be seen in the footage shot by Di Giorgio.
"The debris from the collapsed (bridge) fell 20 meters from my car," Ricci said, adding that he was driving south along the nearby river road at the time. "The central pylon crumbled, then the rest came down."
Emergency services, including the fire department, police, ambulances and mountain rescue teams including sniffer dogs, soon arrived at the site. Several hours later, around 200 firefighters were still working at the scene, according to the Italian fire service.
Luca Cari, spokesman for the fire service, told Italian news agency Rai that rescuers were searching for people underneath the rubble as if it were an earthquake.
Canine search-and-rescue units were deployed by the Italian Red Cross to look for victims beneath the debris, while other Red Cross teams were sent out in police boats to search for people potentially stranded in the estuary of the Polcevera River.
Giorgio Larosa posted a video on Instagram showing rescuers working in heavy rain to free people from crushed vehicles in a grassy area below the viaduct.
Later Tuesday, Giorgio Mascione posted a video on Twitter showing the large gap between the two remaining sections of the viaduct, and the piles of rubble beneath.
Italian Prime Minister visits Genoa
Writing on Twitter shortly after the collapse, Infrastructure Minister Danilo Toninelli described the incident as "an immense tragedy" and said the government was in close contact with Autostrade, the motorway operator.
Italian Prime Minister Giuseppe Conte arrived in Genoa late Tuesday afternoon; he planned to oversee the continuing rescue operation, according to a statement provided by his office.
Several cabinet ministers, including Deputy Prime Ministers Luigi Di Maio and Matteo Salvini, were also traveling to Genoa Tuesday or planning to arrive Wednesday.
Donald Tusk, President of the European Council, sent his support via Twitter. "My heart and thoughts are in #Genoa with all the victims, their families and loved ones," he wrote.
Questions raised about bridge
It is currently unclear why a section of the bridge collapsed. Also known as the Polcevera Viaduct, the Morandi Bridge was designed by Italian civil engineer Riccardo Morandi and completed in 1968. The cable-stayed bridge had a total length of 1.1 kilometers and is 100 meters tall at its highest point.
The collapse came after 15 to 20 minutes of torrential rain, thunder and lightning strikes. An automated report from the weather station at the nearby Genoa Cristoforo Colombo Airport around the time of the incident recorded thunderstorms with winds gusting to 57 kilometers per hour (35 miles per hour).
Some local residents are also questioning whether the bridge was adequately maintained.
"It is too early to say what caused the tragic collapse, but as this reinforced and pre-stressed concrete bridge has been there for 50 years it is possible that corrosion of tendons or reinforcement may be a contributory factor," said Ian Firth, former president of the UK-based Institution of Structural Engineers, and a structural engineer specializing in bridges.
He added that there were "no obvious signs" as to what triggered the collapse at this time and that the storm and ongoing work on the bridge may or may not be relevant factors.
Demitrios Cotsovos, associate professor at the Institute of Infrastructure and Environment at Heriot-Watt University in Scotland, also urged caution before drawing any conclusions.
Engineers should be looking at the impacts of aging on the structural integrity of bridges such as this as well as "the potential impact of the environment and extreme weather conditions."
"Potentially, there are lessons to be learned from such an event," Cotsovos said.
This story has been corrected to reflect that the city of Genoa is located in northern Italy.