At least 16 people have been killed in an attack on a mosque in the southern Afghan city of Kandahar, with reports that Kabul's police chief was among the dead.

According to Kandahar deputy police chief General Salim Khan, the bomb exploded at the entrance to the Mullah Abdul Fayaz Mosque on Wednesday as people entered the building to pray at a funeral.

Interior Ministry spokesman Lutfullah Mashal put the toll at 16 dead and 36 wounded and said an investigation had begun.

An AFP journalist who witnessed the blast, Sohaib Safi, said Kabul police chief General Akram Khakreezwal was among the dead, adding that an unknown assailant dressed in a police uniform had blown himself up immediately upon entering the building.

Safi also estimated that more than 20 people had been killed or wounded in the explosion that targeted the funeral of a Muslim cleric who was shot dead by suspected Taliban fighters at the weekend.

Precise casualty figures were difficult as other journalists report that many body parts and clothes were strewn around the building.

However, a Taliban spokesman told AFP he knew nothing about the blast and none of his men had contacted him about it.

Kandahar was a stronghold of the Taliban government that was ousted from power in late 2001 by US-led forces for harbouring al-Qaida leader Usama bin Ladin.

PHOTO CAPTION

Afghan police officers and local residents stand at a mosque after a bomb blast in Kandahar, Afghanistan. (AP)