Flags flew at half-mast over Venice on Wednesday after 21 people, including a toddler, died when a bus careered off an overpass near the city-state and caught fire.
The new electric vehicle, which earlier reports claimed was powered by methane gas, was returning from a day trip to Venice to a camping site when the accident occurred about 7.30pm on Tuesday.
"The bus flipped upside down. The impact was terrible because it fell from over 10 metres," Mauro Luongo, fire brigade commander of Venice, said at the scene.
He said the cause of the crash was not known but "in the impact the electric batteries of the bus caught fire".
Firefighters worked until dawn on Wednesday to remove the wreckage. Later in the morning, traffic slowly passed the spot where the bus burst through a guardrail and a rusted fence.
Mayor Luigi Brugnaro described the site of the crash as "an apocalyptic scene".
"A tragedy has struck our community this evening," he wrote on Facebook.
Luca Zaia, governor of the Venice region, said: "The provisional toll is at least 21 fatalities and over 20 people taken to hospital."
The victims included at least four Ukrainians and a German citizen, according to Venice prefecture.
The injured, including five in serious condition, included French, Spanish, Austrian and Croatian nationals, local officials said.
At least two of the dead were children, Venice prefect Michele Di Bari said, adding that many of those involved in the accident were young.
Mr Zaia described it as a "tragedy of enormous proportions".
Godstime Erheneden was in his apartment near the accident when he heard a crash outside. He rushed outside and was among the first to enter the bus.
“When we went in, we saw the driver right away. He was dead. I carried a woman out on my shoulders, then a man,” Erheneden told the local newspaper il Gazzettino.
“The woman was screaming, 'my daughter, my daughter,’ and I went back in. I saw this girl who must have been two-years-old. I have a son who is a year and 10 months old, and they are the same size," he said.
"I felt like I was holding my son in my arms. It was terrible. I don’t know if she survived. I thought she was alive but when the rescuers arrived they took her away immediately,” Erheneden said
Firefighters said the bus caught fire after careering off a bridge straddling a railway line linking the Mestre and Marghera districts of the northern Italian city.
Rescuers said the fact that the bus was electric contributed to the massive fire and made rescue operations more difficult.
Corriere della Sera newspaper said 19 people died at the scene, with two dying in hospital.
Italian Prime Minister Giorgia Meloni expressed her "profound condolences".
"I am in contact with Mayor Luigi Brugnaro and [Transport] Minister Matteo Salvini in order to follow the news of this tragedy," Ms Meloni said.
Cause of the accident
The Italian bus driver, Alberto Rizzotto, was killed in the crash.
Venice prosecutors are trying to establish whether he had taken ill while behind the wheel. He was an experienced driver, Venice city councillor Renato Boraso said.
Corriere della Sera reported the bus swerved off the bridge after smashing through a barrier and fell near railway tracks about 15 metres below.
The newspaper said it caught fire after hitting some power lines.
Francesso Moraglia, the Patriarch of Venice, visited the site where he blessed bodies covered with white shrouds on which bouquets of red flowers had been placed.
German Foreign Minister Annalena Baerbock said she was "deeply saddened by the terrible bus tragedy … in this night of grief, my thoughts are with the victims, their families and friends".
In 2017, 16 people on a bus carrying Hungarian students died in an accident near the northern city of Verona.
And in 2013, 40 people were killed in one of Italy’s worst vehicle accidents when a bus plunged off a viaduct close to the southern city of Avellino.