LAGOS — Rescuers are working through the night in search of survivors in the Nigerian city of Lagos after a 22-story high-rise block collapsed during construction, BBC reported.

At least four people have died and dozens are missing.

A digger is at the scene and rescue workers and some locals are searching through rubble and twisted metal. Four survivors have been found so far.

Earlier, pictures from the site showed crowds near a huge mound of debris.

What caused the collapse and exactly how many people are trapped under the rubble remains unclear.

In the meantime, local authorities have ordered an investigation into the collapse and pledged to make the final report public.

Femi Adesina, a special advisor to President Muhammadu Buhari, said the president "commiserates with families who have lost loved ones".

He added that the president had urged the authorities to step-up their rescue efforts.

The building came down at around 14:45 local time (13:45 GMT) 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 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.

Construction worker Eric Tetteh, 41, told the Associated Press that his teams had been waiting for an excavator to arrive at the site when the building suddenly fell.

"Me and my brother, we escaped, but more people are there - more than 100 people," he said.

A witness who was working in an office building opposite the site told the BBC's Outside Source program that he heard a sound, looked out of his window and "saw the building literally going down floor by floor."

Local authorities have put an emergency rescue plan into place, and local officials have visited the site.

But according to AP, Lagos' deputy governor Femi Hamzat was met by crowds of angry people who accused authorities of not starting rescue efforts soon enough.