The five-storey building in downtown Diyarbakir, the largest city in the mainly Kurdish southeast, collapsed after a powerful explosion blamed on a defective heating system.

Four of the victims were children, one of them a newborn girl.

Five people -- two janitors and three men who repaired the heating system on Sunday -- were detained for questioning on suspicion of "accidental manslaughter," Diyarbakir prosecutor Durdu Kavak said.

Police are looking for traces of explosives in the wreckage, although the possibility of a bomb attack is "very weak" and investigators are "95-percent sure" a problem with the boiler caused the explosion, he told reporters.

Diyarbakir is a hotbed of the separatist Kurdistan Workers' Party (PKK), which regularly targets the security forces.

No link has been found between the five detainees and the PKK, Kavak said.

Six people survived the accident with injuries, officials said.

Diyarbakir is home to a major military garrison comprising thousands of troops.

Turkey maintains a strong military presence in the southeast, where it has been fighting an armed PKK campaign for Kurdish self-rule since 1984.