Emergency workers in Tanzania's main city, Dar es Salaam, have now pulled at least 30 bodies from the ruins of a collapsed multi-storey building.The building, which was under construction in the Kariakoo area of the city, collapsed on Friday, crushing a number of cars.Among the dead were construction workers and children who had been in a playground nearby.At least four people are being held by police in connection with the incident.President Jakaya Kikwete visited the scene on Friday and ordered the authorities to take action against those responsible for the collapse.The regional commissioner of Dar es Salaam, Saidi Mecky Sadicky, put the number of dead at 34, saying 10 bodies had been found overnight on Sunday."We will continue looking for more bodies and perhaps we will find more," he told AFP news agency.He said the emergency teams had managed to excavate the rubble up to the ground floor level but added: "We will go on until we reach the basement of the building."There is little hope of any survivors being found in the rubble.The collapsed building was near a mosque, as well as other residential and commercial properties in central Dar es Salaam.It was supposed to have been at least 12 floors high when finished.Tanzania's growing economy has prompted a construction boom in Dar es Salaam in recent years, as in many African cities.But correspondents say the speed of construction and lack of safety standards sometimes put at risk both the buildings and those living and working in them.