Three children, including a newborn baby, are among 21 people confirmed to have died after a tourist coach veered off an overpass near Venice before plummeting 15 metres and bursting into flames. The cause of the crash is not yet clear, although one theory is that the driver, who also died, had suffered a sudden illness. “From the initial findings there are no signs of braking,” Marco Agostini, a Venice police chief, told the Ansa news agency. “The driver’s illness is a hypothesis.” The coach was carrying a group of tourists of several nationalities, who were returning to a campsite after spending the day in Venice. Among the victims were four Ukrainians, one German and a woman whose nationality has not been ascertained, according to the prefect of Venice, Michele Di Bari. Another of the children confirmed to have died was a 12-year-old. Fifteen people were injured, including four Ukrainians, a German, a French person, a Croatian, two Spanish people and two Austrians, Di Bari said. Four of the injured, aged between 20 and 30, were in intensive care, TGCom24 reported. Officials said the vehicle fell on to electricity lines and caught fire at about 7.45pm local time on Tuesday. Local officials initially said that the bus was powered by a methane-diesel hybrid system, and Italy’s interior minister, Matteo Piantedosi, claimed that methane may have been an “aggravating factor” in the bus catching fire. However, the Italian news agency Ansa later reported that the bus in question was an all-electric model. The manufacturer of the bus, China’s Yutong, last year sold 20 all-electric buses to La Linea Spa, the company that owns the crashed vehicle. Yutong was approached for comment. A bus industry expert said the force of the blow from a drop from that height meant there would be a high risk of fire regardless of the fuel type. Di Bari told Sky Italia television that the bus was “totally crushed” and firefighters had trouble getting bodies out of the wreckage. Piantedosi, said on Tuesday night that the coach “flew 30 metres”. However, an officer at the scene said it dropped about half that height. Massimo Fiorese, the chief executive of La Linea Spa, said: “Nobody knows exactly what happened. From what I’ve seen of the images, you can see the bus arriving at less than 50km/h, you see the stop lights come on, so he would have braked. Then you see the vehicle leans against the guardrail, overturns and falls down.” Luca Zaia, the president of the Veneto region, said news of the crash made his “blood run cold”. “We are faced with a tragedy that has few equals in Europe,” he added. The Venice mayor, Luigi Brugnaro, said the city was in mourning for “the enormous tragedy that struck our community and in memory of the numerous victims. It is an apocalyptic scene. I am speechless.” The Italian prime minister, Giorgia Meloni, expressed her “deepest condolences for the serious accident that occurred in Mestre” on Tuesday night. “Our thoughts go out to the victims and their family and friends,” she said. European leaders also sent their condolences. “Our thoughts this evening are with the Italian people, the families and loved ones of the victims of this terrible tragedy,” said the French president, Emmanuel Macron. Ursula von der Leyen, the president of the European Commission, expressed her condolences to the families of the victims and those injured, and her thoughts to Italy’s leaders in what she described as a “moment of great pain”. Charles Michel, the European Council president, said: “I am deeply saddened by the terrible bus accident in Mestre this evening.”