At least 16 students were killed on Friday when a school in central Nigeria collapsed on pupils taking exams.

Trapped students cried for help under the rubble after the Saint Academy school in Jos North district of Plateau State fell in on classrooms.

Parents desperately looked for their children as rescue workers tried to reach the victims with heavy machinery. Images from the scene showed crowds gathering round a caved-in concrete building and heaps of debris.

Officials have so far only said "several students" were killed but a witness saw five dead bodies in one hospital morgue and 11 in another. All were wearing school uniforms.

With his mother at his hospital bedside, injured student Wulliya Ibrahim said: "I entered the class not more than five minutes, when I heard a sound, and the next thing is I found myself here."

"We are many in the class, we are writing our exams," he said.

The National Emergency Management Agency said the two-storey building housing Saint Academy collapsed killing "several students."

It said it had completed the search and rescue operation and would provide details later.

Chika Obioha, a resident at the scene, said he saw at least eight bodies at the site and that dozens more had been injured.

"Everyone is helping out to see if we can rescue more people," he said.

At least 15 rescued and injured students were admitted to the Our Lady of Apostles Hospital.

It was not immediately clear what caused the collapse but residents said it came after three days of heavy rains in Plateau. (AFP)