At least 25 people have died after a school bus plunged into a ravine in Cape Verde.

At around 9 p.m. local time on Saturday, Sept. 5, a school bus carrying mostly teenagers crashed and plummeted 100 feet into a ravine on the Campanas de Cima route in Fogo Island, regional outlets Expresso das Ilhas, A Nação and Demócrata reported.

The students were returning from a field trip in Chã das Caldeiras organized by the bus driver when the crash occurred, according to the outlets. The cause of the incident is unknown at this time.

São Filipe Mayor Nuías Silva confirmed on Saturday that 25 people were killed in the crash, including the bus driver. According to A Nação, Demócrata and the Associated Press, seven of the victims were immediately buried due to their conditions.

Fogo in Cape Verde.Getty
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Rescue and recovery operations are underway after several people were ejected from the bus in the crash, while others remained trapped inside the vehicle, according to Expresso das Ilhas. The rocky ravine has made the search particularly difficult for rescuers.

According to The U.K. Sun, the bus was transporting schoolchildren from Curral Grande and Ponta Verde. Around 19 of the victims were sent to São Francisco de Assis Regional Hospital, with four in “serious condition.”

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São Filipe’s Municipal Council said in a translated statement on Facebook, “In light of this painful tragedy, which resulted in the loss of human lives and left several people injured, the Municipality of São Filipe wishes, first and foremost, to express its deepest solidarity with the families of the victims, their colleagues, teachers, the educational communities, and the entire population deeply shaken by this event…”

Fogo in Cape Verde.Getty
“The City Hall informs that it currently maintains a team in the field, in close coordination with the Health Department, the National Police, the Municipal Volunteer Fire Department (MVFD) and other competent authorities, in order to ensure immediate assistance to the victims and their respective families,” the statement added.

The council declared two days of national mourning following the tragedy.

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President of Cape Verde José Maria Neves called the incident “a great catastrophe” in a translated statement on Facebook.

“I offer my condolences to the bereaved families, to the friends of the victims, and to the island of Fogo,” he said.

PEOPLE has reached out to Mayor Silva, Cape Verde’s Nation