Broad Street in the downtown Lagos Island district was completely filled with rubble and police had cordoned off the area around the Nigerian Industrial Development Bank building while firefighters searched for survivors.
"They have evacuated one dead person and 24 seriously injured to the hospital. We are still looking for ten more people we believe may be trapped in the building," said Lagos State Health Commissioner Leke Pitan.
The first eight storeys of the building, which remained standing, are a car park while the upper floors formed one of Lagos' tallest office blocks.
Building manager Kunle Adebajo, a former president of the Nigerian Institute of Structural Engineers, said the building was supposed to have been sealed off since Sunday, when a fire broke out on the eighth floor.
"It was purely an accident. It's the work of a fire that happened from
Sunday night to Monday morning," he explained.
Witnesses said, however, that security staff had been kept in the building and that a small number of employees involved in critical financial transactions had also been at work when the roof came down.
"I was very lucky to have escaped. I was on the second floor when the building started to fall. I heard the loud noise and electricity went off. I made my way out from the darkness," said generator technician Segun Badmus.
"Those still trapped are security men and some workers in an office in the building who carry out daily transactions with the Central Bank of Nigeria," said a security guard.
The death toll from the collapse could have been much higher, but Lagos has been placed under a daylight curfew during a five-day national census and the city centre's normally teeming streets were standing eerily silent.
Lagos State's planning and urban development commissioner, Hakeem Gbajabiamila, said that the census had also hampered rescue attempts.
"Our limitation is that today is a work-free day. But we are trying to see how we can get a crane that could get to where those trapped are so that they could come out safely," he said.
In recent years dozens of Lagos residents have been killed as the poorly maintained structures in the centre of this city of 14 million people collapse, including at least seven who died in January.
Once the busy centre of Africa's most populous and oil-rich nation, Lagos Island's star has declined as government has moved to the new federal capital Abuja and business decamped to more upmarket addresses on nearby islands.