Rescuers are searching for survivors in the wreckage of a 22-storey block that collapsed under construction in Nigeria’s largest city, Lagos. Authorities say at least 15 people have died and dozens more are missing. Rescue workers at the site say they have heard more voices from under the rubble. Nine people have been pulled out alive so far. The partially built block of luxury apartments came down on Monday but what caused the collapse remains unclear. The building came down in the upmarket district of Ikoyi. It was part of a complex named 360 Degrees Towers, which was intended to house luxury apartments, town houses and penthouses, according to the development’s website, which has since been taken offline. The housing scheme is being developed by Fourscore Homes Limited, which has a portfolio of projects in the UK, US, South Africa, and other areas of Nigeria. While it remains too early to say what caused the collapse, Lagos emergency management agency manager, Femi Oke-Osanyintolu, suggested that some building infractions may have been committed during construction. Local authorities have ordered an investigation into the collapse and pledged to make the final report public.