The clashes were the first since a new government made up of Musharraf's opponents was sworn in just over a week ago.
The violence erupted when supporters of Musharraf held a protest against an attack on Sher Afghan Niazi, a former minister, by lawyers in Lahore a day earlier.
"Our lawyers were staging a protest against an attack on Sher Afgan Niazi. Some other lawyers attacked the group, 10 were injured including a woman lawyer," Faisal Sabzwari, MQM politician, said.
Television footage showed a policeman firing shots in the air to disperse angry mobs who were setting fire to cars and petrol pumps.
|Dozens of cars and buses were set ablaze |
during the riots in Karachi [AFP]
Dozens of rioters also burst into a barristers' room at a district courtroom in the east of the city and set it ablaze but there were no casualties, legal officials said.
Television reports said a bank had also been burned down.
Yousaf Raza Gilani, the new prime minister, condemned the violence and "appealed to the citizens of Karachi to remain calm and peaceful," according to a statement by his office.
Karachi was already tense following an assault on Arbab Ghulam Rahim, a Musharraf supporter and former chief minister of Sindh, on Monday as he was coming out of the city's provincial assembly.
Lawyers have waged a campaign against Musharraf since he first tried to dismiss Iftikhar Chaudhry, the supreme court chief justice, in March last year.
Last November, the president finally sacked Chaudhry and dozens of other judges when he imposed emergency rule for six weeks.
The judges were expected to rule on the legitimacy of his re-election in October while still remaining army chief.
The new coalition government, led by the Pakistan People's Party of assassinated former prime minister Benazir Bhutto last month promised to reinstate the judges.
Chaudhry and nine others were freed from house arrest late last month.
Musharraf has become increasingly isolated after a crushing defeat of his allies in February 18 elections.