Around 20 people were wounded when a blast struck outside a police building early Friday in Turkey's southeastern city of Diyarbakir, the centre of the country's Kurdish minority, security officials said.

The explosion occurred just hours after police detained the two co-leaders of the country's main pro-Kurdish party and several other MPs in a major escalation of a broader crackdown against leading Kurds.

An AFP reporter said that several ambulances were dispatched to the scene of the blast, the cause of which was not immediately clear.

Earlier Friday, police detained Selahattin Demirtas of the Peoples' Democratic Party (HDP) at his home in Diyarbakir while his co-chairperson Figen Yuksekdag was held in Ankara as part of a terror investigation, the state-run Anadolu news agency said.

Their detention appeared part of a large-scale operation against the HDP, which is the third largest party in the Turkish parliament with 59 seats and the main political representative of the Kurdish minority.

NTV television said the pair were accused of spreading propaganda for the outlawed Kurdistan Workers Party (PKK) while Anadolu said Demirtas was accused of provoking violence in deadly protests in October 2014.

The raids come as Turkey remains under a state of emergency imposed in the wake of the July 15 failed coup, which critics say has gone well beyond targeting the actual coup plotters.

Thirteen staff from the opposition Cumhuriyet newspaper, including the editor-in-chief, were detained on Monday, further heightening strains in Turkish society.

Tensions have surged in the Kurdish-dominated southeast since a fragile ceasefire declared by the PKK collapsed in 2015.

It has since stepped up its insurgency against the Turkish security forces, staging regular attacks that have claimed hundreds of lives among the military and the police.

The HDP seeks to promote the cause of Turkey's Kurdish minority and defend the rights of Kurds as well as those of women, gays and workers.