In a house-to-house search operation here, Pakistani paramilitary troops detained over 300 people for questioning in the wake of a surge in ethnic and political violence in the city that claimed nearly 30 lives.
The paramilitary Pakistan rangers launched the search operation in the restive Orangi Town area this morning and detained over 300 people for questioning, local media said.
However, local residents claimed that about 600 people had been detained.
Contingents of paramilitary personnel kept guard during the search operation and people were asked to stay indoors.
All markets, hotels and patrol stations in the area were closed. local residents said children could not go schools as the entire area was sealed.
Troops cordoned off the area and vehicles were banned from entering Orangi Town during the operation. Motorcycle riders faced identity checks.
Officials said more search operations were expected to be conducted in other sensitive areas of Karachi.
Residents had mixed reactions to on Tuesday's operation. Some welcomed the move and others said the operation was causing problems for the general public.
Following the recent spate of killings in Karachi, the Pakistan rangers have been given the same powers as police to conduct search operations, set up check points and detain and investigate suspects.
Earlier, interior minister Rehman Malik had said that a partial curfew would be imposed in parts of the city to facilitate operations by security forces.
According to a strategy framed at a meeting chaired by Mr Malik, aerial surveillance will be intensified and helicopters will be used to air drop police commandos during snap operations.
Authorities have already banned pillion riding on two-wheelers as several recent killings were carried out by motorcycle-borne gunmen.
People have been asked to carry their identity cards at all times to avoid inconvenience during operations by security forces.
The latest spell of violence since Thursday has left nearly 30 dead, including a reporter of the Geo News channel and a former deputy mayor.
Much of the violence has been blamed on rivalry between groups representing Urdu-speaking people and a growing number of Pashtuns. The Urdu-speakers traditionally back Muttahida Qaumi Movement while Pashtuns support Awami National Party.
Both political parties are members of the PPP-led coalitions at the Centre and in Sindh.
Interior minister Malik has claimed that a "third force" is trying to engineer a split among the PPP, MQM and ANP. He did not identify these elements.