At least 21 people were killed and 18 injured in a fiery bus crash in Mestre, Italy, just across the Venetian Lagoon from old Venice, where firefighters and other emergency responders worked into the night trying to extract bodies and squelch the flames.

The bus was carrying foreign tourists, including Ukrainians, according to a Venice official, when it fell from an elevated street Tuesday en route to a camping site near the community of Marghera.

鈥淭he people in the bus found themselves surrounded by flames, 鈥� said Mauro Luongo, commander of the Venice firefighters team. 鈥淭he scene we found was terrible. It took about one hour to extract some of the bodies.鈥�

Venice Mayor Luigi Brugnaro wrote on X, the social media platform formerly known as Twitter, that the crash scene was 鈥渁pocalyptic鈥� and declared the city in a state of mourning.

Four of the injured were in serious condition following the accident, which happened on the mainland just 9 km (3.7 miles) northwest of the old city of Venice, said Renato Boraso, a Venice city official. Two of the dead were children, Venice prefect Michele Di Bari said.

The injured were transferred to five different hospitals in the region.

According to local media, the bus fell a few meters before crashing close to Mestre鈥檚 railway tracks, where it caught fire.

The Veneto region governor, Luca Zaia, told RAI state television that the cause of the accident was still unclear.

鈥淭his is an important tragedy, but it鈥檚 difficult to understand how it happened,鈥� he said. 鈥淭he bus was new and electric, and that street wasn鈥檛 particularly problematic.鈥�

In 2017, 16 people on a in an accident near the northern city of Verona. And in 2013, in one of Italy鈥檚 worst vehicle accidents when a bus plunged off a viaduct close to the southern city of Avellino.