Hasan Akgun, the mayor of Buyukcekmece, told CNN Turk TV he had seen five bodies from the crash, adding that seven people had been aboard the private aircraft.
Provincial Governor Vasip Sahin confirmed the number of casualties.
The Sikorsky helicopter had earlier taken off from Ataturk Airport, to the east of Buyukcekmece, and was headed for Bilecik province in northwest Anatolia.
Buyukcekmece is situated on the northwestern side of the city and contains an industrial area and residential neighborhoods.
The E5 highway, which runs through the district, was closed after debris landed on the road.
There was no immediate official cause given for the crash, which happened at around 11.30 local time (0830GMT), but Cemal Canpolat, the provincial head of the Republican People’s Party (CHP), said the crash was related to foggy weather conditions.
Initial reports said the helicopter crashed into a television tower.
Kugu Aviation, the company which operated the helicopter, identified four of passengers as Aleksandr Vanin, Igor Kochergin, Luidmila Chuprova and Elena Badragan -- all Russian nationals.
A fifth passenger was Turkish national Salim Ozen and the pilots were named as Alaattin Nacar and Ahmet Bulut.
Eczacibasi Holding, a conglomerate focused on building products, healthcare and consumer products, said the helicopter was carrying two of its staff -- Ozen, its Russia director and Vanin, a regional sales manager.
The other three Russians were customers, Chairman Bulent Eczacibasi told reporters. He said the group was in Turkey to attend a ceramics, bathroom and kitchen fair and was heading for Eczacibasi Holding’s facility in Bilecik.
An investigation is underway.