At least 51 killed as bus plunges into ravine in Guatemala

At least 51 people were killed as a bus plunged into a ravine early Monday in Guatemala City, officials said.

At least 20 more were seriously injured, they said.

City officials said the incident occurred when the bus veered off a highway and went into a ravine.

Photos released by fire officials showed the bus upside-down in the ravine as they pulled passengers from the wreckage.

In a statement, Guatemalan President Bernardo Arevalo said the country's army and disaster relief agency would aid in the response.

Arevalo also said he would declare a period of national mourning.

"I stand in solidarity with the families of the victims who today woke up to heartbreaking news. Their pain is my pain," he said.

ABC News' Aicha El Hammar Castano and Will Gretsky contributed to this report.