"It is believed that many people including children are currently trapped in the building," he said. "The third floor of the building is housing a private school in the area," said Farinloye, adding that the three-storey building came down at around 10 a.m. local time.
Workers on top of the rubble shovelled debris away as thousands of people swarmed around the rescue site -- dozens watching from rooftops and hundreds more packed into the surrounding streets, according to a Reuters reporter. The building was in the Ita-faji area of Lagos island, the original heart of the lagoon city before it expanded onto the mainland.
Nigeria is frequently hit by building collapses, with weak enforcement of regulations and poor construction materials often used. In 2016, more than 100 people were killed when a church came down in southeastern Nigeria. In Lagos that same year, a five-storey building still under construction collapsed, killing at least 30 people.
A floating school built to withstand storms and floods was also brought down in Lagos in 2016, though nobody was reported injured. (Reporting by Nneka Chile in Lagos; Additional reporting by Paul Carsten and Camillus Eboh in Abuja and Ola Lanre in Maiduguri; Editing by Catherine Evans)