The bomb went off at Kuchlak Bazar this morning near the venue of a rally organised by a political party.
An eight-year-old girl was among the dead, officials and witnesses told the media.
Witnesses said the blast was followed by firing.
It could not immediately be ascertained who was responsible for the firing.
No group claimed responsibility for the blast, which occurred hours before an official visit to Quetta, the capital of Balochistan province, by Prime Minister Raja Pervez Ashraf.