The seriously injured victims were taken to Kenyatta General Hospital, where six were in critical condition, said Dr. Samuel Ngiru, who works in the trauma department. "If we do not get more blood, people will die," he said.
"Some were lying down for a nap. They were too tired after working for at least six hours," food vendor Jane Wanjiru, 32, said. "We felt the building shake and those of us who were on the roof top jumped onto the roof of the next building. We then watched it collapse."
Immediately after the collapse, hundreds of people formed lines to carry away chunks of concrete and wooden scaffolding, which a front-loader then pushed away from the site. Dozens of soldiers, firefighters, police officers and Kenya Red Cross workers worked to free those trapped.
Construction workers said more than 280 construction workers were inside the building in central Nairobi. By nightfall, it was unclear how many were still trapped in air pockets and parts of the basement, officials said.
Dr. Gilbert Oburu, who was coordinating emergency treatment for survivors, said he saw five dead bodies at the site. Four additional people died while undergoing treatment, a hospital spokesman said.
Oburu said rescue workers brought out at least 68 survivors. They dug frantically into the rubble with bare hands, metal-cutters and crowbars to reach more survivors who shouted through drainage pipes and holes cut in the concrete. One person called a relative using a cell phone and said that he was alive under the concrete-and-steel rubble.
Officials at the scene called the rescue efforts risky and chaotic. Hands of those waiting to be rescued could be seen waving from beneath the rubble, reports CBS' Alison Harmelin.
Tens of thousands of people ran to the site, clogging the roads and climbing on top of the rubble to watch the rescue. Riot police deployed to the area and beat back crowds with truncheons, clearing roads for emergency vehicles.
President Mwai Kibaki announced he was cutting short an official visit to Sudan in order to coordinate rescue efforts, according to a statement.
Rescue workers were running out of oxygen to administer to survivors as they were being pulled out of the rubble. There were also not enough power saws and other pieces of heavy equipment, Joshua Toro, assistant minister for roads and public works, said after talks with emergency workers.
The British government agreed to send a special team with rescue dogs and high-tech equipment, but their arrival was delayed until Tuesday afternoon, said Abbas Gullet, the secretary-general of the Kenya Red Cross.
By nightfall, most of the onlookers had gone home. Professional rescuers set up lights and continued digging for trapped survivors at different places around the building. Meanwhile, a large bus with apparently failed brakes crashed through the medical triage area, injuring one medic and slamming into a parked ambulance.
One construction worker, who would not give his name, said an inspector had warned last week that the structure was not safe and they were trying to stabilize the building.
"This is all about building standards," said Kenyan Army Brig. George Kyaka, who was leading the military response. "But those who are alive are the priority now."
"It is very important that we put in place mechanisms to ensure that only properly designed buildings are built," said Vice President Moody Awori, who visited the scene to check on the rescue effort.
Most of injuries occurred during the building collapse, but some were injured during the stampede that followed, when Nairobi's normally crowded streets turned into chaos. A two-year-old boy, Ngiru said.
"I was coming home from school when I heard a whoosh and people started running, and I was pushed over," Evans Omolo, 11, said while clutching his broken arm at the hospital. "I couldn't see what was happening, but people were jumping on me as they ran past."