The demonstrators were protesting against a parliamentary proposalto change the name of the North West Frontier Province, or NWFP, to Khyber-Pakhtoonkhwa.
The name change was pushed in part by the Awami National Party, a Pashtun nationalist group that leads the provincial government in the northwest.
But the violent protests have temporarily delayed the scheduled presentation of a constitutional reform bill to change the name to the upper house of parliament.
Proponents say the bill is designed to strengthen parliamentary democracy and give greater power to the provinces, as well as replace the British-colonial name of North West Frontier Province.
The lower house of parliament voted through the 18th amendment in a unanimousvote last week.
But many non-Pashtun groups in the northwest, including the area's ethnic Hazara population, have opposed the idea.
Al Jazeera's Kamal Hyder, reporting from the city of Abbottabad, said the 18th amendment has become a real problem for Pakistan.
"The people of Hazara say that renaming the province is going to divide the province," he said.
"They say that it should remain as the [NWFP], otherwise they say they should have a second province called Hazara.
"Yesterday, peaceful protesters were out on the streets. But they say the police opened indiscriminate fire, killing eight people on the spot.
"The protesters ... are saying they will not accept the agenda of renaming this province."