At least three people have been killed and dozens more are trapped after a multi-storey building collapsed in the centre of the main Tanzanian city, Dar es Salaam, rescue workers say.
Thirteen people have been pulled out of the ruins alive, officials say.
Some 45 people, including construction workers, residents and children from a Koranic school, are 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."
Our reporter says a huge crane has been pulling out a mass of iron bars to get access to the centre of the building, where some people are thought to be still alive.
Trapped victims are said to have been making phone calls to friends and relatives.
Bulldozers are also being used to move the rubble, our reporter says.
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.