As slogan chanting crowds began assembling outside the Sindh High Court, riot police attempted to break them up by baton charging and bundling lawyers into police vans, as the country's most prominent opposition leader Nawaz Sharif declared "we are ready for the long march."

Vowing to join the marchers in Lahore, Sharif accused the government of plotting to kill him, but said he won't be deterred to bring back Pakistan on the road to democracy.

Among those arrested here were Ghafoor Ahmed, Vice President of Jamaat-e-Islami and Athar Minallah, leader of the local bar Association.

Ahead of the march, seen as a political show-down between erstwhile allies PML-N leader Nawaz Sharif and Pakistan President Asif Ali Zardari, authorities throughout the night continued their swoop rounding up scores of political leaders, right activists and lawyers in a bid to thwart the march.

Organisers are hoping that hundreds of thousands of lawyers, opposition supporters and civil activists will join the four-day convoy on the 1,500 kilometres (940 miles) to Islamabad, where it is supposed to arrive on Monday.

The protesters want President Asif Ali Zardari to act on his promise to reinstate judges sacked in 2007 by former military ruler Pervez Musharraf, including Supreme Court chief justice Iftikhar Muhammad Chaudhry.

Though police warned the lawyers of the Karachi bar association, which has been playing a key role in organising the protest, they would be arrested if they violated the restrictions, hundreds of them defied the orders.

Thousands of lawyers, rights activists and workers of opposition parties like the PML-N, Jamaat-e-Islami and Pakistan Tehrik-e-Insaf are to join the "long march".

The protesters are to set-off from different parts of Sindh and Balochistan, moving in convoys towards Punjab province, a stronghold of the PML-N.

Protesters from different parts of Pakistan are scheduled to congregate in Punjab before marching to Islamabad, where the protest will culminate with a sit-in outside parliament.