The "march for independence," organized by the Tehreek-e-insaaf (PTI) political party expected to bring a crowd of 100,000.
Khan's convoy was attacked as his convoy passed through the town of Gujranwala on its way to Islamabad.
According to television reports, members of the prime minister's party, Pakistan's Muslim League-N party, threw stones at the convoy. Khan claimed that his car was also struck by gunfire, although that claim could not be confirmed.
Khan posted on Twitter Friday that "PMLN workers attacked again but I have asked our workers to remain calm and peaceful."
PMLN workers attacked again but I have asked our workers to remain calm and peaceful.— Imran Khan (@ImranKhanPTI) August 15, 2014
Sheikh Rasheed Ahmed, an ally of Khan, remarked Friday that "civil war has broken out" and called for the prime minister to resign. "They will have to leave the government. The army must intervene."