An Islamic State suicide bomber killed 57 people including women and children and wounded dozens outside a voter registration centre in the Afghan capital Kabul on Sunday in the latest attack on election preparations.

The assaults underscore growing concerns about security in the lead-up to legislative elections scheduled for October 20, which are seen as a test-run for next year's presidential poll.

"It happened at the entrance gate of the centre. It was a suicide attack," Dawood Amin, Kabul police chief, told AFP.

Both the health and interior ministries confirmed the latest toll for the attack, which was claimed by Islamic State of Iraq and the Levant (Isil) via its propaganda arm Amaq.

After initial reports, the death toll from the blast rose to 57 on Sunday afternoon, with 119 others wounded, a public health officer said.

The centre in a heavily Shia-populated neighbourhood in the west of the city was also being used by people to register for national identification certificates, which they need to sign up to vote.

Sheets of paper and passport-sized photos lay scattered amid shattered glass and pools of blood on the street near badly damaged cars - grim evidence of the force of the blast that drew international condemnation.

"This senseless violence shows the cowardice and inhumanity of the enemies of democracy and peace in Afghanistan," US ambassador John Bass wrote on Twitter.