The cause of the collapse is unclear, but it appears that the taller building fell onto a smaller one.
Emergency services remained at the scene into Sunday evening.
Samuel Ivaha Diboua is the Governor of the Littoral region, who stated, “A 4-storey house collapsed, and we recorded 31 people, 12 of whom died.”
“The others are currently in hospital receiving medical treatment.”
As rescue workers search the remnants of the two apartment blocks, it is thought the death toll could rise.
Local residents said the incident occurred around midnight, but it was not until the early hours of the morning that emergency services arrived.
A worker who had been repairing the building said: “I was sleeping and received a call at about five past midnight, but I didn’t pick it up.”
“At about 00:30, I woke up and realised people had been trying to reach me. Then I heard the news which is so tragic.”
“There were some signs of problems, but we were working on it, we were working on the perimeter of the building.”
One local hospital reported treating 13 cases arising from the tragedy and recorded two deaths, including “a three-year-old girl and a 19-year-old girl.”