A tragic bridge collapse in Genoa, Italy has claimed the lives of at least 35 people according to authorities.

NBC News reports a large section of the Morandi Bridge collapsed at around 11:30 am local time in heavy rain. The exact cause of the collapse remains unclear, but a witness told ANSA that the bridge was hit by lightning shortly before it came crashing to the ground.

Experts say a lightning strike probably wasn’t responsible for the collapse and a representative of the motorway’s operator, Autostrade, told Reuters “The collapse was unexpected and unpredictable.” Stefano Marigliani added, “The bridge was constantly monitored and supervised well beyond what the law required.”

There are conflicting reports about how many vehicles were on the bridge at the time of the collapse, but estimates range from as little as 33 to as high as 40. Regardless of the final number, authorities are having a difficult time getting to victims as the 80 meter (262 feet) section of bridge crashed onto buildings below.

The scene is now a massive rescue and recovery operation as hundreds of police officers and fire fighters are looking for victims and survivors. They are being assisted by specially trained dogs and heavy equipment which is being used lift pieces of rubble.

The bridge dates back to the 1960’s and the part that collapsed was reportedly 50 meters (164 feet) off the ground. While initial speculation focused on the age of the bridge, Reuters said that restructuring work was carried out in 2016. However, the BBC says worked continued on the bridge and Autostrade was shoring up the bridge’s foundation at the time of the collapse.