Angry supporters of slain opposition leader Benazir Bhutto took to the streets of Pakistani cities on Thursday, from the Himalayas to the southern coast.
The unrest was predictably fiercest in Bhutto's native Sindh province and its capital, Karachi.
"Police in Sindh have been put on red alert," said a senior police official.
"We have increased deployment and are patrolling in all the towns and cities, as there is trouble almost everywhere," he said.
Reports said security was deteriorating in Karachi, where thousands poured on to the streets to protest. At least three banks, a government office and a post office were set on fire, a witness said.
Tyres were set on fire on many roads, and shooting and stone-throwing was reported in many places. Most shops and markets in the city shut down.
At least 20 vehicles were torched in the central Sindh town of Hyderabad.
There were also small protests in Rawalpindi and the nearby capital, Islamabad.
Protesters blocked roads with burning tyres and chanted slogans against President Pervez Musharraf in Muzaffarabad, capital of Pakistani Kashmir in the mountainous north.
Police said they had been ordered to block the main road between Punjab province and Sindh province, apparently to stop the movement of protesters.
Disturbances were also reported in the southeastern city of Multan, although details were sketchy. In the eastern city of Lahore, Bhutto party workers burnt three buses and damaged several other vehicles, police said.
Trouble was reported from the interior of Sindh province, including the Bhutto ancestral home at Larkana, police said.
"The situation is not good in the interior of Sindh. A large number of people have come out on the roads in many cities to protest," said senior police official Fayyaz Leghari.
(Editing by Roger Crabb)