Provincial police chief Abdul Razaq said a motorcycle-riding bomber detonated his explosives near a crowd of civilians and truck drivers, most of whom were transporting NATO supplies, CNN reported.
A second round of explosives detonated when people were rendering aid to victims of the first blast, Razaq said.
The attacks occurred near the Kandahar airfield, the base for NATO troops in the region.
The Taliban claimed responsibility for the bombing and said two vehicles were used, The New York Times reported. One was an explosives-packed trailer attached to a motorcycle and remotely detonated and the other was another motorcycle, spokesman Qari Yusuf Ahmadi said.
Kandahar province is considered the birthplace of the Taliban and has been the scene of pitched fighting between insurgents and coalition forces.
The International Security Assistance Force said coalition forces at the Kandahar airport were never in danger, saying a government spokesman indicated the bombs were placed deliberately to injure Afghan shopkeepers.
ISAF officials said insurgents were responsible for more than 1,000 civilian casualties to far this year.