People are feared to be trapped in the ruins of a 21-story building that collapsed in Lagos, Nigeria on Monday.

The building, located in the city's affluent Ikoyi neighborhood, is a construction site for luxury apartments. It is unclear how many people were inside when it fell.

"I thought it was an earthquake when I rushed out of my apartment just after 3 p.m. I felt the building move and knew something was wrong," Olu Apata, a nearby resident and the president of the Nigerian Bar Association stated.

Apata said the building has been under construction for the past two years and that the developer was at the site meeting with prospective buyers earlier on Monday.

Muhammad, a civil servant, said he was in his office next door when the high rise came down.

"We just heard an unusual loud sound from our office building and the building we're occupying was vibrating. So, I looked through the window, only to see the building collapsing floor after floor. And of course, we all ran to safety."

Hours after the collapse, hundreds of people were milling around the site, helplessly surveying slabs of concrete piled high in a heap. Locals were digging through the wreckage by hand.

Some in the crowd were furious that an official emergency response had not started. Instead, rescue efforts were being carried out by passersby such as Rashid Olamilekan, who told reporters he had pulled three construction workers from the rubble.

"I am a Nigerian. I have to rescue my people," he said.

The rescued workers had been taken to the hospital, Olamilekan added.  

The Nigerian Red Cross is also now at the scene.

Building collapses are a relatively common occurrence in Lagos, Nigeria's largest city with a population of around 20 million people.

In 2019, the collapse of two separate buildings, including one housing a school, left dozens of people dead.

An expert at the time said that more than 1,000 buildings were at risk of collapsing in Lagos.

CNN