Rockets were fired and grenades lobbed as violence wracked the city with thousands of people stranded in their home in fear of flying bullets.
Police and rescue officials said that in four days 88 people had been killed with some 200 wounded in target killings and indiscriminate firing in many parts of the city, owing to political as well as ethnic clashes.
Struck by the magnitude of incidents in Karachi, the US Embassy in Islamabad today said it is deeply concerned about the escalating violence in the port city.
"We call on all parties to refrain from further violence and work toward a peaceful resolution of differences," Ambassador Cameron Munter said in a statement.
"The loss of over 60 lives, including women and children, in the last three days is a tragedy." Karachi has been rocked by violence despite the presence of President Asif Zardari in the city where he is stationed at the Bilawal house and has held meetings with his aides to discuss the situation.
Interior Minister Rehman Malik, who rushed to Karachi yesterday, said that 1000 additional militia force will be deployed to restore normalcy in the city.
He also said that "targeted actions" will be taken against the miscreants without any political discrimination.
"We have received satellite images about those who have made bunkers and actions are being planned against them," Malik told reporters in Karachi where he attended a meeting of senior police and paramilitary military commanders.
The authorities have ordered shoot-at-sight order in Karachi as violence has paralysed life in the city, police said.
Meanwhile, the city today gave a deserted look as the main powerful ethnic group declared mourning over the recent wave of violence.
Public transport is missing and people faced problems to find transport to reach offices, residents said.
President of the transport union, Irshad Bukhari, said that transporters had decided not to bring vehicles as the Mutahida Qaumi Movement or MQM had declared mourning.
"Several vehicles had been burnt, buses hijacked and divers killed," Bukhari said, adding "we can not run buses in this situation.
"Almost all main markets and patrol stations were also closed and educational institutions postponed papers." In a new trend of violence that has left the people in total fear and helplessness, armed men have resorted to firing on public transport and in some parts of the Orangi town, residences were attacked with rockets and hand grenades even as few houses also being set on fire.
"As the government prepares to take decisive action against these miscreants indiscriminate firing started again from the hills surrounding Orangi Town with Qasba colony and Baldia the worst hit," a rescue official said.
All main shopping centres, offices and banks remained closed while petrol pumps had shut down since last night.