At least one person has been killed and more than 100 arrested ahead of rallies over Pakistan's continuing judicial crisis in the southern city of Karachi.
Thousands of security personnel are deployed in the city
Demonstrations are planned for Saturday when Pakistan's ousted top judge is due to address his supporters in the city.
Chief Justice Iftikhar Chaudhry was suspended by President Musharraf in March. He denies abuse of power.
The suspension triggered protests by lawyers and the opposition which have grown into an anti-government campaign.
Observers say anger over the judge's suspension poses the biggest challenge to Gen Musharraf's rule since he seized power in 1999.
The BBC's Syed Shoaib Hasan in Karachi, capital of Sindh province, says lawyers there plan a massive reception for the chief justice on Saturday.
Opposition political parties - including the six-party MMA Islamic alliance and the country's largest party, the Pakistan People's Party - are also expected to participate.
The ruling party in Sindh, the Muttahida Qaumi Movement (MQM), has said it will hold rival demonstrations in support of President Musharraf's government on the same day.
More than 15,000 security personnel have been deployed in the city to prevent violence.
Late on Friday morning, a security guard was shot dead by armed men forcibly closing down a shopping centre on Karachi's main thoroughfare, Shahrah-e-Faisal.
Mr Chaudhry was suspended from his post in March
Earlier, police arrested scores of political activists and raided homes across the city.
"We have detained over 100 people who are a risk to security on 12 May," Azhar Farooqi, the city police chief, told the BBC.
"We are monitoring the situation and there may be more arrests required."
The city and provincial police are controlled by the home department which is headed by a minister from the MQM.
But the party leadership denies that it has used the state machinery to help keep the opposition in line.
"I assure you the MQM will follow the law to the letter and never indulge in such tactics," Dr Farooq Sattar, a senior MQM leader, told the BBC.
He described such suggestions as "last resort propaganda".
Both sides have refused to reschedule their rallies, and the lawyers have accused the provincial government of using intimidatory tactics.
Ahead of the 12 May rallies, Munir Malik, a leader of the lawyers' campaign to have the chief justice reinstated, had his offices sealed by local building officials.
The courts later suspended the move. Hours later, his home was attacked by unidentified gunmen.
Since then there has been a visible increase in tensions in Karachi, which has a long history of political violence, our correspondent says.
Both government and opposition politicians have called for restraint.