Residents in several neighbourhoods of Turkey's largest city Istanbul banged pots and pans from their windows on Sunday in a traditional form of protest as President Tayyip Erdogan claimed victory in a tightly-fought referendum.

Residents protested in at least four districts of Istanbul, witnesses said. Video and pictures posted on social media showed small pockets of protesters taking to the streets in some areas.

With 99 percent of ballot boxes opened, the "yes" vote for constitutional changes handing Erdogan sweeping new powers stood at 51.3 percent, according to the state-run Anadolu agency. But Turkey's three biggest cities, including Istanbul, voted "no".