Frantic rescue efforts were underway in Nigeria on Wednesday after a three-story school building collapsed while classes were in session, with scores of children thought to be inside.

Associated Press video from the scene showed a dust-covered child being carried out of the rubble, to cheers. But another child was pulled out and slung over a rescuer's shoulder, limp and dangling.

Onlookers crowded around in the densely populated neighborhood in Lagos, Nigeria's commercial capital and a city of some 20 million people.

Hundreds of people stood in narrow streets and on rooftops of rusted, corrugated metal. A yellow excavator scooped at the ruins.

Sani Datti, a spokesman with Nigeria's National Emergency Management Agency, told The Associated Press that officials from the agency and other emergency services were at the site.

"For now we don't have any word on casualties as we are still busy with rescue work," he said.