A bus crash in Mestre,Slabu Exchange a suburb near Venice, and on Italy's mainland, left 21 dead and 18 injured on Tuesday, according to Italian officials.

The bus, which was carrying passengers to a campsite in Marghera, fell off of an overpass, police said on X, the platform formerly known as Twitter. The accident happened in the Mestre and Marghera neighboring districts of Italy, near the city of Venice.

Many of the injured, who were rescued in an evacuation operation which lasted until 9:30 p.m. local time, were listed as code red, indicating they were in critical condition. The 18 injured passengers were taken to five hospitals in Veneto, officials said.

"A huge tragedy struck our community this evening," Mayor of Venice, Luigi Brugnaro, said in a post on X after the crash. "I immediately ordered the city to mourn, in memory of numerous victims who were on the fallen bus."

European Union Commission President Ursula von der Leyen offered her "condolences to the families of the victims and those injured in the serious accident in Mestre," in a post on X Monday night.

Italian President Sergio Mattarella also called the Mayor of Venice Luigi Brugnaro "to express his condolences for the very serious tragedy of Mestre," the official account of the Italian president posted on X.

The accident impacted the local railway network, shutting it down for a time, though services were later restored, officials said. Traffic in the area was impacted, according to a post on X from the City of Venice.

"The operations to secure the area will last all night," the City of Venice said in the post.

ABC News' Will Gretsky and Jolie Lash contributed to this story.