One man then says: "We shall only release you after the struggle".
24 hours after the abduction, survivors say that armed men broke into the facility in the early hours of Monday morning.
Paul Biya's inauguration on Tuesday for a seventh term as Cameroon's president is eclipsed by the search for 79 school pupils kidnapped by English-speaking separatists.
The school's principal and a teacher were also kidnapped by people who don't want a ransom, but rather want remaining students to be sent home, sources tell The Guardian.
A video purportedly of the kidnapped children has been released on social media via men who call themselves Amba boys, a reference to the state of Ambazonia that armed separatists are trying to establish in Cameroon's north-west and south-west regions.
The government and English-speaking separatists have accused each other of orchestrating the kidnapping.
A six-minute video seen by AFP, but which could not be immediately confirmed independently, showed 11 boys apparently aged about 15 giving their identity and name of the school in English, and adding that they were abducted by the "Amba Boys" - the name for anglophone separatists.
China motorway toll crash: At least 15 dead in Lanzhou
The semi-trailer was registered to Li's home northeastern Liaoning province, more than 2,000km from the scene of the incdient. Deadly road accidents are common in China, where traffic regulations are often flouted or go unenforced.
The conflict between the insurgents and government security forces intensified previous year after a government crackdown on peaceful protesters. But it reported that some parents said on social media that they recognized their children in the video.
An American missionary also died in the North West region near its capital, Bamenda, when he was shot in the head amid fighting between separatists and soldiers.
According to United Nations figures, 246,000 people in the Southwest Region have fled their homes, and 25,000 have sought shelter in neighbouring Nigeria, many of them living hand-to-mouth in the forests.
In an October presidential election, opposition candidate Maurice Kamto declared victory against Biya, who has ruled since 1982, but Biya's ruling party dismissed claims of defeat and accused Kamto of breaking the law.
What have the kidnappers said?They have torched at least a hundred schools and chased students and teachers from schools that they then take over as training grounds.
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Around a fifth of Cameroon's 22m people are English-speaking - a minority whose presence dates back to the colonial period.
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