The collapse of a school building in Lagos killed 20 people, a health official said Friday.
At least 45 others who were in the building at the time of the collapse survived.
The previous death toll provided by authorities was eight.
It was not yet known what caused the collapse of the building containing a school on Wednesday in a crowded neighbourhood at the heart of 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 neighbourhood on Thursday, marking other derelict buildings for demolition.
Obiora Manafa with the Standards Organization of Nigeria told reporters that 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."
A crowd of hundreds of people had cheered on 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 groaning, inefficient infrastructure in Africa's most populous nation.