"This morning a roadside bomb hit their vehicle killing eight, including four women," Panjwayi governor Fazal Mohammad Eshaqzai told AFP, adding that two children were wounded.
An interior ministry statement confirmed the blast and said the victims belonged to one family.
There was no immediate claim of responsibility, but roadside bombs are a common weapon used by the Taliban, though attacks that kill civilians often go unclaimed.
According to a UN report released Wednesday, civilian casualties in Afghanistan soared by 24% to 4,853 in the first half of 2014 compared to the same period in 2013.
Ground combat is now causing more deaths and injuries than improvised explosive devices (IEDs) in a worrying sign of spreading conflict, the UN report said, with women and children increasingly caught in the crossfire.
The grim figures underline the fragile security situation Afghanistan faces as it wrestles with political turmoil over its disputed presidential election, with most foreign forces due to withdraw by the end of the year.