Twelve persons, including nine children, have been confirmed dead in the three-storey building that collapsed in the Ita-Faaji area of Lagos Island.
As part of effort to rescue the trapped pupils who were wailing under the rubbles, men of Lagos State Emergency Management Authority, LASEMA, Lagos State Fire Service, and other rescue teams have been dispatched to the scene.
"It is believed that many people including children are now trapped in the building", he told the BBC.
The children were attending a nursery and primary school on the top floor of the residential building when the structure collapsed.
"This incident has further highlighted the urgent need.to take urgent action on issues of safety in schools across the country", country director Hussaini Abdu said.
"HURIWA also called for the forensic audits of all public building assets including malls; stadia and places of worship to safeguard the lives of millions of Nigerians in Lagos".
Also reacting to the incident, Lagos State Building Control Agency LASBCA, said the building that caved in had been marked for demolition since a year ago because it was discovered by the Agency to be distressed.
3-story building collapses in Nigeria with children inside
It's gathered that over 100 pupils are feared trapped.
Workers have pulled more than 40 people, dead and alive, from the ruins.
"Please, save my child, save my child!" wept one traumatised mother whose seven-year-old daughter was trapped inside, as people tried in vain to console her.
Building collapses are frequent in Nigeria, where regulations are poorly enforced and construction materials are often substandard.
In September 2014, 116 people died when a six-storey building collapsed in Lagos where a celebrity televangelist was preaching. In 2016, a church roof caved in on a crowded congregation in Uyo, a city in southern Nigeria, killing at least 160 people.
A floating school built to withstand storms and floods also collapsed in Lagos in 2016, though no injuries were reported.