Clashes broke out on Friday as tens of thousands of protesters from two anti-government movements converged on Pakistan's capital, Islamabad.
Gunshots hit the vehicle of former cricket star and opposition politician Imran Khan as he led his supporters through the eastern city of Gujranwala.
Residents brandishing ruling-party posters attacked his convoy, throwing shoes and stones. Mr Khan was not injured, his spokeswoman said.
Mr Khan and populist cleric Tahir ul-Qadri are slowly leading separate processions towards Islamabad where they plan to occupy main streets until Prime Minister Nawaz Sharif resigns, Reuters reports.
The protests are a major challenge for Pakistan's 15-month-old civilian government at a time when the nation is fighting an offensive against Pakistani Taliban militants and the influence of anti-Western and sectarian groups is growing.
In the latest violence, 10 militants were killed and 13 members of the security forces were wounded in attacks on two air force bases in the city Quetta late on Thursday, the third time since June that airports had been targeted.
Mr Qadri, a cleric and political activist who usually lives in Canada, has accused police of killing 22 of his supporters during clashes in the eastern city of Lahore in June and August. Police confirmed 11 deaths.
About 2000 of his supporters were also arrested in August, police said.
Mr Khan is protesting against alleged electoral irregularities in last year's polls.
Army may play referee
How far Imran Khan and Tahir ul-Qadri succeed in destabilising the government is likely to depend on the stance taken by a military with a long history of mounting coups.
Few people think there will be a coup but many officials fear the threat of unrest will increase the military's hold over the government.
Most observers expect the military to play referee, to maintain security but not support action to force Nawaz Sharif out.
"Imran will not get from the army what he was expecting," an analyst close to the military told Reuters.
"If there was any confusion earlier about whether the army would help Imran or rescue him or topple the government, there should be none now. There is no question of army intervention."