Kurdish militants launched a truck bomb attack on a police station in southeast Turkey overnight, killing six people and wounding 39 in one of the biggest strikes since conflict flared in the region last July, security officials said on Thursday.

The blast ripped the facade off the building in the small town of Cinar and caused extensive damage to the surrounding area, smashing windows, mangling shop shutters and littering the streets with debris, a Reuters witness said.

The mainly Kurdish region has been hit by a surge in violence since a two-year ceasefire between the state and the Kurdistan Workers Party (PKK) collapsed six months ago, reviving an insurgency that has killed 40,000 people over three decades.

The conflict is stretching Turkey's security forces, which are fighting on two fronts. The latest blast follows a suicide bomb attack by a suspected Islamic State militant which killed 10 German tourists in Istanbul on Tuesday.

PKK militants attacked the police station and adjoining accommodation in Cinar, south of the main regional city of Diyarbakir, at around 11:30 p.m. (2130 GMT), the provincial governor's office said in a statement.

There was no immediate claim of responsibility for the attack, in which the statement said five people were killed. The Reuters witness saw a sixth dead body pulled from the wreckage and a security source said it was that of a policeman's wife.

"It was a really loud blast, as if it was in our house," said Ali Devran, a resident in his 30s near the scene. "We went and helped carry the wounded to ambulances. Some suffered burns."

A security source said 1.5 tonnes of explosives were used in the blast. Rescue workers continued to search for bodies at the scene, where ambulances remained on standby.

Deputy Prime Minister Numan Kurtulmus condemned the attack as "treacherous" on his Twitter account.

Simultaneous gun attack

Coinciding with the bomb attack, PKK fighters opened fire with rifles on a nearby security complex, triggering a firefight, but no casualties were reported, the statement said.

The relatives of two police officers were killed in the attack, along with three people whose bodies were pulled from the wreckage, it added. Six police officers were among the wounded being treated in nearby hospitals.

The PKK, designated a terrorist group by Turkey, the United States and the European Union, says it is fighting for autonomy and greater rights for Kurds in the NATO-member country.

Since the PKK launched its insurgency in 1984, fighting has stayed largely in the countryside, but the latest violence has focused on urban areas, where the PKK youth wing has set up barricades and dug trenches to keep out security forces.

Towns along the Syrian and Iraqi borders, along with a district of Diyarbakir, have been subjected to round-the-clock curfew for more than a month, as operations by security forces have targeted militants there.

Civilians have been caught in the middle. Figures from the pro-Kurdish HDP party show 87 civilians have been killed in Diyarbakir's Sur and two towns near the southern borders since they were placed under curfew last month.

Thousands of people have left their homes in the towns. Residents complain of indiscriminate operations and say the curfews have even prevented the sick from getting to hospital.