Police headquarters under attack in southeast Turkey
The bomb attack caused immense damage to the headquarters of the special anti-riot police force in Cizre, with television pictures showing an immense plume of black smoke heading into the sky.
There was no immediate information on possible casualties but television quoted the health ministry as saying 12 ambulances and two helicopters had been sent to the scene.
Early pictures showed that the police building had been rendered completely unusable by the power of the blast, reduced to a shell surrounded by a pile of rubble.
The state-run Anadolu news agency said the bomb had gone off 50 metres (yards) away from the building at a control post. It said the blast had been carried out by the PKK.
The Turkish security forces have been hit by near daily attacks by the PKK since a two-and-a-half year ceasefire collapsed in 2015, leaving hundreds of police and soldiers dead.
The PKK has kept up its assaults in the last weeks even after the unsuccessful July 15 coup by rogue elements in the military aimed at unseating President Recep Tayyip Erdogan.
Turkey on Thursday shelled the Kurdish militia fighters in Syria, saying they were failing to observe a deal with the US to stop advancing in jihadist-held territory.
Ankara sees the Kurdish Democratic Union Party (PYD) and its People's Protection Units (YPG) militia as terror groups bent on carving out an autonomous region in Syria and acting as the Syrian branch of the PKK.