The clashes between the Ahle Sunnat Waljamaat members and the Shiites happened in the town of Bhakkar in Punjab province, police official Abdullah Khan said.
The conflict followed a protest rally held by the Sunnis after one of their members was gunned down while closing his shop.
People were killed on both sides, Khan said.
Pakistan has experienced worsening sectarian violence in recent years, especially attacks by radical Sunnis targeting Shiites.
Also today, gunmen on a motorcycle opened fire outside a Sunni seminary on the outskirts of the capital, Islamabad, killing two people and wounding a third, police official Mohammad Bashir said.