At least two people were confirmed dead and dozens feared trapped after a building under construction collapsed in Tanzania's main city of Dar es Salaam on Friday.
Hundreds of people, including residents and army rescuers, clawed through piles of rubble in an affluent area of the country's economic capital in the hunt for survivors.
The building collapsed as many people including children were working or playing nearby, witnesses said.
"I thought there was an earthquake and then I heard screaming. The whole building fell on itself," witness Musa Mohamed told AFP.
Dar es Salaam regional police chief Suleiman Kova said the rescue operation was "going well".
"So far we have managed to retrieve 19 people. Two of them are dead and are two seriously injured," he said as he briefed Tanzanian President Jakaya Kikwete during a visit to the scene.
Kova said that although it was too early to establish the cause of the accident, "the owner of the building would be held responsible and taken to task".
Scores of people were reportedly working in and around the building at the time of the incident at around 8:45 am (0545 GMT).
Residents told AFP that during normal working days, the area bustles with activity from a mix of business people, passers-by and playing children
"My children normally come to play here during Sundays and holidays. I am not sure whether they are also trapped," one desperate local resident Elizabeth Richard told AFP through tears.
Next to her, rescue workers were dragging out pieces of wood, iron rods, chunks of sand and bricks from the 20-metre high piles of rubble with the hope of locating more survivors.
"I was terribly shocked with the strange noise," said Ramadhan Issa, a taxi driver who was having tea at a nearby restaurant at the time of the disaster.
"It will take us several hours to reach the pockets we suspect to have survivors," police officer Lameck Kundya told AFP.
Saidi Mecky Sadiky, the Dar es Salaam regional commissioner, said up to 60 people, including workers, food vendors and children could have been around the area, which has a mixture of both commercial and residential developments.
Kikwete posted messages of condolence on his Twitter account.
"We pray for those who have been afflicted by this tragedy. We pray for togetherness in this time of need," Kikwete said.
In 2008, another building collapse in Dar es Salaam claimed at least four lives.
"It looks like the city authorities are not serious with the enforcement of construction and housing laws. The city is undergoing a construction boom, but incidents of collapsing buildings are on the increase," city resident Rashid Abdallah said.