LAGOS (Reuters) - At least one person was killed and dozens of children were among those feared trapped after a four-storey building containing a primary school collapsed in Nigeria’s commercial capital Lagos on Wednesday.

Adeshina Tiamiyu, general manager of the Lagos State Emergency Management Agency, said that the agency had recorded one death so far in the disaster, and had rescued nearly 50 people.

“We will be able to give total figures in the morning after we have cleared to the ground floor,” Tiamiyu said.

Workers on top of the rubble shoveled debris away as thousands of people swarmed around the site to watch, many of them angry or distraught. Police, ambulances, Red Cross workers, fire trucks and a fork lift were on the scene.

Residents said around 100 children had attended the school, which was on the top levels of the building.

A Reuters reporter saw a boy of 10 being pulled from the rubble, covered in dust but with no visible injuries, and the crowd erupted into cheers as another child was pulled out.

A spokesman for the National Emergency Management Agency’s southwest region said many people, including children, were believed to be trapped.

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Lagos Governor Akinwuni Ambode visited the site and offered condolences to bereaved families. Ambode said the school had been set up illegally and that buildings in the area had been undergoing structural testing prior to the accident.

The collapsed building is in the Ita-faji area of Lagos island, which was the original heart of the lagoon city before it expanded onto the mainland.

One bereaved relative, Bose Adeshida, said she had two nieces, aged 11 and 4, who attended the school. The elder child, Amoke, died and her younger sister was being treated for head injuries, Adeshida said.

It was not clear if her dead niece, who had attended the school since the age of 2, was the same person cited by the Lagos emergency agency as having died in the collapse.

Adeshida, whose younger sister was the mother of the children, said she was angry because people had complained about the building for the last 12 years.

She said the site had been marked for demolition but developers repainted it and rented out the space.

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“It is expensive in that area. That’s why people stay in a building like that,” she said.

Local resident Yomi Olaniyi, 42, said four buildings had collapsed in the area in the past few years.

Outside the hospital where people taken out of the building were taken for treatment, anxious relatives sobbed and ran toward ambulances as they arrived, hoping their loved ones were inside. Some fell to their knees with tears streaming down their faces.

A Google photograph of the collapsed building from early 2017 shows no sign of a school inside. The fourth storey only had the words “Olulade Villa (Psalm 27)” painted across its balcony.

Presidency Muhammadu Buhari said in a statement he was “extremely saddened” by the building collapse.

Building collapses are frequent in Nigeria, where regulations are poorly enforced and construction materials are often substandard.

In 2016, more than 100 people were killed when a church came down in the southeast, and in Lagos the same year, a five-storey building collapsed, killing at least 30 people.

A floating school built to withstand storms and floods also collapsed in Lagos in 2016, though no injuries were reported.