Italian authorities were on Wednesday investigating the cause of a horrific bus crash near Venice that killed at least 21 people including two children.
A spokesperson for the Italian fire brigade told CNN that authorities had yet to find the cause of Tuesday's crash in Mestre that was described as an "apocalyptic scene."
RAI reported that the 40-year-old bus driver, identified as Alberto Rizzotto, was among the dead, while 18 people were also injured.
Italy's fire services said they would consider whether the bus's battery may have caused the fire to spread more rapidly after it overheated.
According to the company website of the bus operator, the bus was electric-powered.
The provincial fire brigade commander, Mauro Lungo explained batteries experience "critical issues" when they overheat, CNN affiliate Sky TG24 reported Wednesday.
According to Lungo, concerns about the battery slowed down the rescue operation on Tuesday. Meanwhile the Venice public prosecutor has opened an investigation into the crash.
A representative for the prosecutor's office told CNN the head prosecutor for the Venice municipality, Bruno Cherchi, is leading the investigation into the incident in Mestre.
Video recently delivered to investigators is being examined to determine if any other vehicles were involved in the incident or if the driver suffered a health issue, the spokesperson said.
The bus was traveling from Venice to nearby Marghera and was "full of people returning home from work," Venice mayor Luigi Brugnaro told state media RAI.
"It completely went off the road, it flew off the bridge. It was a bus; it was a highway. We are in mourning," he added. Brugnaro described the scene as "apocalyptic" in a post on Facebook.
The accident occurred on the overpass of a road that leads from Mestre to Marghera and the A4 motorway, Italian media skytg24 reported.
For reasons that have yet to be determined, the bus broke through a wall of the overpass, falling between a warehouse and the tracks of the Mestre station below, according to skytg24.
Massimo Fiorese, the head of the company that operates the bus, said he had seen footage of the moments prior to the crash.
The video showed the single-decker bus slowing down and appearing "almost stationary" before crashing through the guardrail and toppling over, he told Italy's Corriere della Sera newspaper, according to Reuters.
On Wednesday morning, the Italian Senate, which is the upper house of the parliament, held a minute of silence for the victims of the crash, its feed on X said.
The country's president and prime minister expressed their condolences in the aftermath of the accident as did other world leaders.
"I express my personal and the Government's deepest condolences for the serious accident that occurred in Mestre. Our thoughts go out to the victims and their family and friends," Italian Prime Minister Giorgia Meloni wrote on X.
French President Emmanuel Macron said "thoughts this evening are with the Italian people, with the families and loved ones of the victims of the terrible tragedy in Venice" in a post on X.
"I am deeply saddened by the terrible accident of a bus in Mestre this evening. I offer my deepest condolences to the families and loved ones of the victims at this sad time. I'm close to you," President of the European Council, Charles Michel, wrote on X.