As some anguished families protested and sifted through the rubble for any sign of their children, National Emergency Management Agency official Ibrahim Farinloye said workers had reached the foundation of the collapsed three-story building and did not expect to find more victims.
He declined to give an updated toll of the dead and rescued. Officials late Wednesday said 37 people had been rescued from the rubble.
An unknown number of people remained missing. Frantic efforts had gone into the night to find signs of life in the debris.
Scores of families waited anxiously at hospitals in Lagos for updates on their loved ones. Adeyemo Sunday, the father of twins, mourned one of his sons.
"They were quick to rescue one of the twins, which is Kehinde. By the time they rescued Taye, likely he got hit on the head by concrete, though he got to Mercy Hospital before he died," he lamented.
Sunday said his family lived on the second floor of the building and he sent his boys to school there so they wouldn't have to travel far. He was at work when the building collapsed, he said at Lagos General Hospital.
At the same hospital, Yewande Ogunsanwo said her son remained in critical condition.
"Let's thank God for God, he's getting better but his condition is so critical," she said with fear. "The pain is too much."
It was not yet known what caused the collapse of the building containing a school in a crowded neighborhood in Nigeria's commercial capital, Lagos.
Building collapses are all too common in the West African nation, where new construction often goes up without regulatory oversight.
Lagos state Gov. Akinwunmi Ambode said the building, which had been marked for demolition, was classified as residential and the school was operating illegally on the top two floors.
Official moved through the neighborhood on Thursday, marking other derelict buildings for demolition.
Obiora Manafa with the Standards Organization of Nigeria told reporters they would analyze samples of the collapsed building's concrete and steel bars "to ascertain the quality ... and know whether they complied with the national building code."
Hundreds of people had cheered Wednesday as dust-covered, shocked-looking children were carried out one by one. Other small bodies, however, hung limp over workers' shoulders.
As many as 100 children had been in the primary school on the building's top floors, witnesses said. Some authorities disputed that, but all grieved.
"It touches one to lose precious lives in any kind of mishap, particularly those so young and tender," Nigerian President Muhammadu Buhari said.
The collapse came as Buhari, newly elected to a second term as president, tries to improve the distressed infrastructure in Africa's most populous nation.
AP reporter Sunday Alamba contributed to this report from Lagos, Nigeria.
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