The incident occurred in Dasht area of Mastung district, 25 km south of the provincial capital of Quetta, officials of the Levies militia said.
Ten men were killed instantly when the gunmen fired indiscriminately at the group.
All the dead and injured were Pashtuns, Levies officials said.
The injured were taken to Quetta.
The gunmen, who were riding motorcycles, escaped after the attack.
No group claimed responsibility for the attack though such incidents are usually blamed on Baloch nationalist groups.
Balochistan borders Iran and Afghanistan and has been plagued by sectarian and ethnic violence and attacks by Taliban fighters.