A sustained coordinated assault on a government building in the Afghan capital of Kabul has killed 29 people, an interior ministry spokesman has said.

Most of them were employees of the department for martyrs and disabled persons, Najib Danish added.

Another 23 people were wounded, including three policemen.

Afghanistan
Flames rise from a government building after an explosion and attack by gunmen (Rahmat Gul/AP)

The assault began with a suicide bomber who blew up his explosives-laden car in front of the multi-storey building in an eastern neighbourhood of Kabul.

Within minutes of the powerful explosion three gunmen, armed with assault rifles and explosive devises, stormed the building.

For nearly eight hours they rampaged through the office complex terrorising employees.

Afghanistan
Afghan security forces arrive at the site of the attack (Rahmat Gul/AP)

Some of the employees managed to hide and police quickly evacuated 357 other employees, Mr Danish said.

Witnesses reported hearing at least five explosions as police and gunmen traded fire.

One of the dead was a police officer but the rest were civilians including two women.