One person has been killed and several injured in clashes between protesters and security forces on the outskirts of the northern Pakistani city of Gilgit.
An indefinite curfew in the city and in other parts of the country's northern areas remains in force.
There was widespread violence in the town of Hunza when the authorities tried to stop Shia from demonstrating.
They have been campaigning for changes in religious textbooks. The changes are strongly opposed by many Sunnis.
Troops on patrol
A BBC correspondent in Gilgit says that the city has remained mostly peaceful since the imposition of the curfew on Thursday morning.
Our correspondent says there were clashes between demonstrators and security forces on the outskirts of the city, when a radio transmitter compound was attacked.
A police guard room was burnt down by the protestors, but the transmitter is not reported to have been damaged.
Gilgit is a Shia majority area
Throughout the day troops with machine guns mounted on trucks patrolled the city, warning local people not to come out of their homes.
But despite the strict security measures, the authorities were unable to stop a large number of Shia Muslims from nearby villages marching towards Gilgit.
As the protesters tried to enter the city, clashes broke out between armed villages and the security forces.
Doctors at a local hospital said one protester was killed and at least three injured.
Two police officials were also brought to the hospital with gunshot wounds, but their condition was said to be stable.
Reports from the nearby town of Hunza said thousands of Shia protesters attacked government buildings in the morning, and ransacked a state-run hotel. A number of offices were also set on fire.
The were protesting against the government's decision to impose a ban on rallies staged by the Shia community.
They are a minority in most parts of Pakistan, but form a sizeable majority in the country's northern areas.
They have been campaigning for the changes in the curriculum, particularly in textbooks for religious studies, which they say only present a Sunni Muslim version of Islamic history.
The Shia community had planned a big demonstration on Thursday, but because of sectarian killings in Karachi earlier this week the authorities imposed restrictions in an effort to avoid violent clashes between rival communities.
Our correspondent in Gilgit says that it is unlikely that the curfew will lifted in the foreseeable future.
Meanwhile a large number of Shia protesters are still reported to be blocking the main Karakoram highway in Gilgit which links Pakistan with China.