Nigeria ruled out terrorism Monday in a massive blast that flattened a bank building in its largest city, while the death toll rose to 44 after more bodies were pulled from the rubble.

Dozens of workers piloted cranes and bulldozers in a search for survivors in the debris of a Lagos Island building containing a four-story bank and three stories of apartments above. Four more bodies were recovered Monday.

"We're informed that many people are trapped in the collapsed building, but it's unlikely there are any living people there," said Emmanuel Ijewere, president of the Nigerian Red Cross.

More than 60 injured people were recovering in Lagos medical centers, Ijewere said.

The cause of Sunday's explosion remained unclear.

"The preliminary investigation showed it was not an act of terrorism," Lagos State Governor Bola Tinubu said.

Police said earlier they were considering several theories behind the blast, including the possibility that someone was trying to rob the bank.

Lagos city spokesman Dele Alake said investigators were considering various theories, including whether the building's natural gas source ignited or a cache of explosive material stored there detonated accidentally.

Authorities began evacuating six buildings housing hundreds of people near the charred ruins to evaluate them for structural damage, Alake said. Three precariously leaning structures will be demolished.

The force of the detonation shattered windows for blocks around and scattered cash from bank vaults into the air. Several looters were arrested for grabbing the money.

The blast occurred on Lagos Island, a crowded high-rise district of banks and other businesses packed side-by-side with poor, densely populated residential blocks. The island is one of two that, with the mainland, form this city of 12 million people.

Nigeria is Africa's most populous nation, with 120 million residents.