Omar Zwak, a spokesman for the provisional governor, said a child was among the dead, Khaama Press reported.
The blast damaged several vehicles.
Zwak said there were no reports concerning casualties among NATO forces.
No group, including the Taliban, had claimed responsibility for the incident, Khaama Press said.
In Ghazni province, officials reported a heavy explosion near the Ghazni city airport, sending thick, black smoke skyward.
Khaama Press said unconfirmed reports indicated the blast occurred near the Polish military base.
Officials in Kandahar province said an Afghan police officer fired on his colleagues Wednesday in another instance of insider attacks, injuring at least 16 Afghan security forces.
A senior security official said an investigation had begun and that a motive was not known.
Khaama press did not indicate what happened to the assailant.
Khaama Press said insider attacks, also known as green-on-blue attacks, are a key concern for Afghan and coalition security forces. Such attacks have left dozens of Afghan and NATO troops dead in recent years.