Segunbaghicha, Paltan, Kakrail, Karwan Bazar and Hatirpul are among the areas affected by the outage.
Dhaka Power Distribution Company Limited (DPDC) Managing Director Md Nazrul Hasan said a technical fault had developed at the Ulon grid substation at Rampura.
"The repair work is on. I hope everything will be in order within an hour," he told bdnews24.com around 7:30pm Wednesday.
A Segunbaghicha resident said that his area was hit by the outage around 4:30pm and the blackout was persisting even at 8pm.
The situation was the same at Hatirpul, said a resident.
People living in places such as a Rampura, Khilgaon, Basabo and Dhanmondi had suffered six hours of power outage on Aug 28 due to a fault at the same substation.