A livestock truck and a school bus carrying teenagers heading to summer camp collided in central Spain yesterday, killing 27 people, officials said.
The exact number of passengers in the bus and the cause of the accident were not immediately known.
The accident occurred near the town of Soria, about 110 km north-east of Madrid.
Police said the truck, loaded with pigs, suddenly swerved out of its lane and the two vehicles collided head-on. The bus plunged down an embankment.
Emergency crews rushed to the scene and worked frantically to pull survivors from the mangled wreckage of the bus. Ambulances transported the injured, many in serious condition, to local hospitals.
Most of the victims were 14-and 15-year-old students from two high schools in the Barcelona area on an annual summer excursion.
News reports on the number of injured ranged from 15 to 30, and officials said they had not yet pinned down the exact number.
Twenty-two of the victims died at the scene and five others succumbed to their injuries after arriving at hospitals.
Both drivers and a teacher from Barcelona were among those killed, local media said.
Spain's King Juan Carlos and Queen Sofia sent a note of condolence to the children's schools.
Barcelona's Archbishop Ricard Maria Carles expressed his grief for "the magnitude of this tragedy".
Students at one of the schools said they were left behind because there were not enough seats on the bus. "We were lucky," one boy told reporters.
A hospital spokesman in Soria said a team of psychologists was being brought in to help family members and survivors cope with the trauma.
At the scene of the accident, bodies were laid side by side on the pavement, draped in sheets and blankets.
Pigs that had escaped from the overturned truck rooted through fields near the twisted wreckage of the two vehicles.
Sobbing relatives and schoolmates of the victims gathered at their schools. One mother collapsed in a friend's arms.
At least three people fainted and were taken away in ambulances, state radio reported.
Mr Juan Jose Lucas, the president of the surrounding Castilla and Leon region, has declared three days of mourning.
