But neither side wants trouble and they have reached agreement on a designated route through the city, our correspondent says.
The convoy travelled from the city of Lahore on the last leg of the nationwide protest.
The "long march" - as it has been dubbed - has passed through different towns and cities on its way to the capital.
Several thousand lawyers have been joined in the capital by a much larger number of activists, most of them supporters of the PML-N.
Protesters were showered with rose petals as they passed through the city of Jhelum en route to Rawalpindi and the capital.
"These are Musharraf's last days," leading lawyer Aitzaz Ahsan told the crowd.
"We are out in the streets to save Pakistan."
Pakistan's deposed Chief Justice, Iftikhar Chaudhry, and Nawaz Sharif are expected to address the protesters.
President Musharraf dismissed dozens of judges, including the Supreme Court chief justice, in November when he imposed emergency rule. At the time he faced numerous legal challenges to his staying on for another term.
The lawyers' convoy includes hundreds of buses and cars
The move further enraged lawyers and his political opponents, who were already infuriated over his attempts earlier in the year to sack Mr Chaudhry.
The PML-N now argues that the judges should be reappointed by an executive order from the prime minister.
But the PPP wants to link any reinstatement to a major package of constitutional reforms.
The differences led Mr Sharif to withdraw his ministers from the cabinet last month, although his party still supports the coalition government.
The two parties also appear to differ over how to deal with President Musharraf.
Mr Sharif has called for his removal and trial for treason, but the PPP appears wary of a confrontation with the president, who has insisted that he has no plans to resign.
Before the judges were sacked, the Supreme Court was also due to rule on the legality of an amnesty President Musharraf granted former Prime Minister Benazir Bhutto, then the PPP leader, and her husband Asif Ali Zardari.
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