The explosion went off in the district of Baglar in the centre of the city and was a “terrorist” attack, the state-run Anatolia news agency said.
Television channels CNN-Turk and NTV said that at least 15 police had been wounded in the explosion. The Dogan news agency said some civilians in the area were also wounded.
Diyarbakir and its region have in recent months been hit by repeated attacks by the outlawed Kurdistan Workers’ Party (PKK) as the military presses a relentless offensive against the Kurdish militants.
Earlier, two police had been killed in a bomb attack blamed on the PKK in a district of the southeastern city of Van to the east which had so far been spared the worst of the fighting.
Seven Turkish police officers were killed and at least 27 people wounded in late March in a bomb attack on their vehicle in Diyarbakir.
The PKK first took up arms in 1984 demanding a homeland for Turkey’s biggest minority, later paring back its demands to focus on cultural rights and a measure of autonomy.
Over 40,000 people have been killed in the insurgency.
The new upsurge of violence between the security forces and Kurdish militants erupted in July 2015, shattering a two-and-a-half year truce.