The death toll from the collapse of an apartment building in Istanbul rose to 21 on Saturday, as President Recep Tayyip Erdogan said authorities have "lessons to learn" from the incident.
Experts from the Istanbul branch of the chamber of civil engineers who visited the site concluded that the "load-bearing columns had lost the capacity to carry the weight" of the building.
Speaking at the scene, President Recep Tayyip Erdogan said there are "many lessons to learn".
Health Minister Fahrettin Koca has increased the death toll to 17.
The collapse took place at around 4pm on the Asian side of Istanbul in the mostly residential Kartal district.
"Among 13 injured, seven are in intensive care while six are still being treated at our services".
Hopes that more survivors might be found were raised early Friday when a 16-year-old boy was pulled alive from the rubble, the news agency said.
Authorities haven't disclosed how many people remain unaccounted for.
Environment Minister Murat Kurum, who accompanied Erdogan, said the block housed 14 apartments and three businesses.
Fourteen apartments were registered at the site but the top three floors of the building had been built illegally, the city's governor Ali Yerlikaya has said.
Engineers and architects regularly sound the alarm against illegal additional storeys to buildings which they say weaken the constructions' structure, and put them at greater risk in the event of an natural disaster. In January 2017, two people died when another building collapsed in a working-class part of the city.