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A four-storey building being built in the Kenyan capital, Nairobi, has collapsed on top of scores of people, leaving at least four dead.
Passers-by joined professional rescuers in the search
Kenyan TV said 200 people were in or around the building when it fell.
Rescuers have been digging through the rubble with their bare hands to save those trapped inside amid what a BBC correspondent says are chaotic scenes.
A doctor at Kenyatta General Hospital said 67 people had been admitted with chest, leg and abdominal injuries.
The hospital appealed for people to go to the hospital to donate blood, while police called for people trained in rescue operations to make their services available.
Various witness reports from the scene speak of more dead bodies having been found, but so far police have not given an official death toll.
Farid AbdulKadir, head of disaster operations with the Kenya Red Cross Society, confirmed four deaths.
Calvince Omondi, a volunteer rescuer, told AFP news agency that contact had been established with "several" people trapped in the building's basement who were running short of oxygen.
On TV footage, a hand could be seen waving for help from under a concrete beam at the site on the corner of Ronald Ngala St and Tom Mboya St, in the River Road area.
Bulldozers and ambulances have arrived at the scene in central Nairobi, but the BBC's Karen Allen says army and rescue workers are getting caught up in crowds of onlookers and passers-by trying to search the debris.
'I felt a tremor'
A local man said the lower floors of the building had been filled with construction workers, and that work had been going on to add additional floors to the top of the building.
According to a Reuters news agency reporter, some of the concrete was still wet.
Witnesses said at least 50 masons and 50 other workers were among those inside the building when it collapsed at about 1440 (1140 GMT).
"We were working and then I felt a tremor... and then the building just fell," construction worker Patrick Otiyo, who escaped with minor injuries, told Reuters.
According to witnesses quoted by AFP, a large crack appeared in the building before it collapsed.
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