Rescuers on Wednesday were racing to find survivors on the third day after a high-rise building under construction collapsed and trapped scores of people in the commercial capital Lagos, as the death toll rose to 22, officials said.

As hope turned to despair, anxious family members and large crowds gathered near the site of the incident hoping to hear news on the fate of those still trapped under chunks of masonry and mangled steel where the building once stood.

One man, choking with tears, said a relative of his travelled from United States for a wedding in Abuja and had then been invited to Lagos by the developer to look at the building project. He has not been heard from since Monday.

Phone numbers for the project owner, main contractor, project manager, structural engineers and architects listed near the collapsed building, were switched off when Reuters called on Wednesday, suggesting some of them may have gone underground.

Lagos State commissioner for information, Gbenga Omotoso said a six member independent panel of engineers, architects and town planers had been appointed to "ascertain what went wrong and recommend measures to forestall further occurrence."

The panel has a month to present its findings.

The collapsed building, in the affluent neighbourhood of Ikoyi, was one of three blocks that had been planned to be high-end apartments.

At least 22 people have died while nine people have been found alive and treated at hospital, officials said.

Building collapses are frequent in Africa's most populous country, where regulations are poorly enforced and construction materials often substandard.

Lagos Governor Babajide Sanwo-Olu said there was no manifest of who and how many were working when the building collapsed.

"Unfortunately it has also been difficult for us to identify anyone, or anyone to come forward as the project manager, or a staff of the developer or contractor," he said during a visit to the site.

Authorities have said there had been some building infractions during construction earlier this year but did not say whether these had been rectified.

Reuters