Lagos, Nigeria (CNN) Twenty people are now confirmed dead after a three-story building housing a school collapsed in Lagos city in Nigeria, health officials told CNN.

Lagos Health Commissioner Jide Idris told CNN on Friday those that were killed were mostly children from the school.

Lagos State Governor Akinwunmi Ambode said earlier in the week that the school was operating illegally in the collapsed building.

Forty-five people were rescued from the building and are now recovering at various government hospitals in the city, the health commissioner said.

"I'm delighted to note that the survivors of the unfortunate incident are calm, stable and responding to medical treatment and in no time, some of them who are certified and cleared will be discharged to join their families," Idris said.

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