At least 20 people are dead after a bus veered off an overpass near Venice, Italy, on Tuesday evening, authorities said.

Venice Mayor Luigi Brugnaro told Italian state TV channel Rai News24 that there were "at least 20 dead" after a bus veered off the road and fell a few meters close to railway lines in Mestre, a suburb of Venice. Following the crash near railway tracks, the bus caught on fire.

"There are at least 20 dead, but some people are still trapped in the wreckage," Brugnaro said.

Venice prefect Michele Di Bari said that there were 15 survivors from the crash. 

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The cause of the incident is still unclear with emergency crews on the scene accessing the damage.

Following the crash, Brugnaro wrote on X, in a translated post, that the scene of the crash was "apocalyptic" and that he had already ordered the "city to mourn" for the "numerous victims" who were on the bus.

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"A huge tragedy struck our community this evening" Brugnaro wrote. "I immediately ordered the city to mourn, in memory of the numerous victims who were on the fallen bus. 

"An apocalyptic scene, there are no words," he said.

Ursula von der Leyen, president of the European Commission, gave her condolences to residents, saying that she is close with local government during this time of "profound pain."

"My deepest condolences to the families of the victims and those injured in the serious accident in Mestre," Von der Leyen wrote in a translated X post. "I am close to President Mattarella, President Meloni and the mayor of Venice Brugnaro in this moment of profound pain."

Reuters and the Associated Press contributed to this report.