The city's largest community are Mohajirs, descendants of those who fled from south of the border when the 1947 partition separated Pakistan from India. They make up almost half of the population, and tend to support the pro-government Mutaihda Qaumi Movement (MQM). Punjabis and Pathans each make up around a quarter of the population.
The violence that has claimed 41 lives since Saturday and left the city paralyzed by a general strike on Monday began when MQM supporters took to the streets to prevent opposition supporters from welcoming Iftikhar Choudhry, the chief justice sacked by Musharraf two months ago, whose legal challenge to his ouster has become a rallying point for government opponents. Iftikhar was scheduled to attend the 50th anniversary of the Sindh High Court Bar Association in the city, but a couple of days before his arrival, the MQM announced plans to hold a rally at the same time to challenge the opposition groups who were planning to welcome the ousted jurist.
Hours before the competing rallies, local officials used shipping containers and tanker-trucks to barricade all the city's major roads and intersections, blocking access to and from Karachi's Quaide Azam International Airport. Hundreds of young Musharraf supporters, many of them armed with handguns and automatic weapons, then surrounded the majestic pink-stone building of the Sindh High Court where the Chief Justice had been expected to address the legal fraternity. The mob attacked anyone wearing black trousers, a white shirt and a black jacket the dress code of Pakistan's courtroom lawyers.
"I have never seen such things in my life," said Hamid Munir, a high court lawyer. "They stopped my car, smashed its side window panes and snatched my cell phone."
Still, hundreds of opposition supporters defied all warnings and appeared on the streets, dancing and chanting anti-government slogans. As they proceeded towards the airport, they were fired on from bridges and rooftops. Within an hour, Karachi resembled Baghdad, as dozens lay dead and injured on the city's streets, gunmen preventing ambulances from reaching the wounded.
On the streets on Saturday, there was no sign of any effort by police to stop the violence. Local reports claimed that the government had not issued firearms to the police, and that paramilitary rangers were not permitted to intervene. Then, on Sunday the government issued shoot-on-sight orders to the rangers, as violence spread.
The violence was not restricted to supporters of the rival political groups, however. Eyewitness reports from the Malir district of Karachi suggested that MQM militants had rounded up people simply on the grounds that they looked by Pathan or Punjabi, and tried to execute them.
"I begged and pleaded them that I am not an opposition worker; I am a student," says Aadil Badshah, a 20-year-old Pathan studying engineering, who was shot in the legs and hands. "They did not listen to me. They were laughing at us and four others. One of them was a 50-year-old laborer. First they beat us, took us inside a street, put us to stand in a line and then fired on us. And then left. Two died on the spot and me and two others survived."
In another area, armed men killed an ambulance driver and his two injured patients. And as the reports of Pathans and Punjabis being targeted by Mohajirs reached city slums that house most Pathans and Punjabis, angry protesters took to the streets, exchanging gunfire with their Mohajir neighbors and pelting each other with stones.
The Chief Justice himself, who remained stranded for eight hours at the VIP lounge of the airport along with many of his lawyers, returned to Islamabad after local authorities refused to allow him to enter Karachi by road.
Meanwhile, in Islamabad, Musharraf talked tough. "I am not afraid of anyone," he told supporters at a rally in the capital. "People are with me."
The government in Karachi, run by the MQM, quickly announced compensation for the dead and injured $5000 to be paid to the family of each person killed, and $840 for each of the wounded. But it may take a lot more to defuse the crisis.
"It could be na´ve to think that [Musharraf] could personally survive while the country slides into perdition. There are more cracks and fissures in it today than when he took power in 1999," said an editorial on Sunday in English-language Daily Times.
The MQM blames Iftikhar for the violence. "It only started after his arrival in Karachi. Before that the city was peaceful," thundered Altaf Hussain, the party leader who has been living in self-exile in London for the last 15 years, to his supporters over telephone.
The Saturday violence has made Karachi residents wary of an all-out ethnic backlash. Says Faisal Edhi, whose family foundation run's Pakistan's ambulance service, "Everywhere there is fear. Suddenly people are afraid of each other."