Dozens of rescuers dug into the rubble with their bare hands while the injured were loaded into any available car to be taken to hospitals. The hand of one trapped person could be seen waving for help from under a concrete beam.
Tens of thousands of people ran to the site, clogging the roads and climbing on top of the debris to watch the rescue. Riot police deployed to the area began using truncheons to beat back the crowds and to clear roads for emergency vehicles
At the same time, however, police appealed for anyone with emergency training to come to the scene and help the rescue.
Dozens of soldiers, firefighters, police officers and Red Cross workers responded, using crow bars and metal cutters to free those trapped.
An Associated Press reporter at the scene saw eight bodies of those killed in the collapse.
One of the construction workers said that 280 men were on the site. Another, who would not give his name, said an inspector had warned last week that the structure was unsafe and they were trying to stabilize the building.
"We saw the building sink slowly and then sway from side to side. As we saw this, we fled the area. We never got that far — it collapsed," said Serengo Wekesa, who had been working at a neighboring building.
One worker, James Ofunyi, said the workers were on their lunch break, with many asleep in the building when it collapsed.
"I was taking a nap after having had lunch when I heard someone shouting to run, but I didn't get downstairs fast enough because the building started falling," Ofunyi said. "I jumped to the other side."
Immediately after the collapse, hundreds of bystanders formed lines to carry away chunks of concrete and wooden scaffolding, which a front loader then pushed away from the site.
Two survivors were pulled from the building more than an hour after the collapse, prompting the crowds to erupt in cheers. But there were fears that more people were caught between the floors that collapsed on top of one another.
Parts of the exterior walls were still standing.
A nurse at Kenyatta General Hospital said more than 50 people had been admitted. She hung up the phone without identifying herself.
The hospital issued an appeal for blood donations.
The lower floors of the building were filled with construction workers when it suddenly collapsed, said one of the laborers, Patrick Opiyo, who was digging for survivors.
"This is all about building standards," said army Brig. George Kyaka, who was leading the military response. "But those who are alive are the priority now."