At least 17 people have been killed after a multi-storey building collapsed in the centre of the main Tanzanian city of Dar es Salaam on Friday morning, according to a local official.
Commissioner Saidi Meck Sadick said 18 people had survived.
He added that the search for other survivors was continuing.
Earlier reports said some 45 people, including construction workers, residents and children from a Koranic school, were missing.
The BBC's Hassan Mhelela says the high-rise building under construction is now a "huge pile of chaos".
Eyewitness Nishit Surelia told the BBC: "There was a huge noise and the building collapsed behind me.
"Everyone started running, thinking it was an earthquake. There was dust everywhere. We then realised what had happened."
Trapped victims are said to have been making phone calls to friends and relatives.
Tanzanian President Jakaya Kikwete visited the scene.
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.
Police say they are questioning four people linked to the construction company, while work on a nearby site undertaken by the same company has been suspended.
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.