Rescuers on Tuesday pulled four survivors from the rubble of a collapsed building in downtown Nairobi as crews worked feverishly to reach at least four other people believed to be trapped inside, officials said.

At least 14 people were killed in the collapse Monday and dozens were injured, said Army Maj. Gen. Paul Opiyo. The five-story building was filled with construction workers who had just finished lunch and were napping when it began to sway, then quickly tumbled, witnesses said.

Workers struggled throughout the night to cut through layers of concrete using sledgehammers, metal-cutters and crowbars in the search for additional survivors. Many shouted encouragement through drainage pipes and holes in the rubble.

Rescuers did not know the exact number of people still trapped, but they could hear at least four people in two different places in the rubble and were concentrating their efforts in those areas, Opiyo said.

"If there are holes or air pockets, we can save many people," said Maj. Gen. Yitzhak Gershon, leader of an Israeli rescue team that arrived Tuesday to help.

U.S. Marines and Navy engineers based in nearby Djibouti also arrived at the site Tuesday to assist, as did experts from Britain.

About 280 construction workers were at the construction site in central Nairobi when the building came down, survivors said. Officials have accounted for 102 people, including the dead and injured.

Forty-two were in stable condition at Kenyatta General Hospital.

Most of the workers were day laborers and no one has been able to provide authorities with a detailed list of who was at the site.

"We felt the building shake and those of us who were on the rooftop jumped onto the roof of the next building," said food vendor Jane Wanji, 32, who was one of several women who had set up stalls inside the building to sell food to workers and had brought their children with them. A 2-year-old boy was among the injured.

Maj. Gen. Mohammed Hussein Ali, the police commissioner, said detectives have opened a criminal investigation into the incident.

One construction worker, who would not give his name, said Monday that an inspector had warned last week the structure was not safe and they were trying to stabilize it.

Raila Odinga, the main opposition leader and a member of parliament, said those found responsible for the collapse should face the death penalty.

"I suspect the building collapsed because they used poor materials or that the job was rushed," he said.

President Mwai Kibaki said he was cutting short an official visit to Sudan to coordinate rescue efforts.