DIYARBAKIR, Turkey: A strong blast rocked Turkey's largest Kurdish-majority city of Diyarbakir on Tuesday near the riot police headquarters, just days before a key referendum on boosting President Recep Tayyip Erdogan's powers.

The blast could be heard in several areas of the southeastern city, an AFP journalist at the scene said, with medics saying at least four people were wounded.

Grey smoke rose from the area as ambulances rushed to the scene.

The cause of the explosion was not immediately known.

Turks will on Sunday vote on whether to approve constitutional changes giving Erdogan executive presidential powers, which critics say would drag the country into one-man rule.

The southeast has been battered by renewed fighting between Kurdish rebels and Turkish security forces since a fragile truce collapsed in summer 2015.

The outlawed Kurdistan Workers' Party (PKK) has been waging an insurgency against the Turkish state since 1984 during which over 40,000 people have been killed.

The group is designated by Ankara, the United States and the European Union as a terror group. -AFP