Pakistani opposition leader Nawaz Sharif defied house arrest on Sunday to join anti-government protests.
Hundreds of police surrounded the Lahore residence of former prime minister Mr Sharif before dawn on Sunday and detained him along with scores of his supporters.
Officers in the eastern Pakistani city showed party officials an order placing Mr Sharif and his politician brother Shahbaz under house arrest for three days.
But Mr Sharif denounced the order as illegal and later left the house in a convoy of vehicles packed with chanting, flag-waving supporters, headed for a city centre rally.
'These are the decisive moments,' Mr Sharif told supporters before he climbed into his car.
'I tell every Pakistani youth that this is not the time to stay home - Pakistan is calling you to come and save me.'
Senior government official Rao Iftikhar said that authorities had reconsidered the restrictions on Mr Sharif to allow him to address the rally and return home afterward.
Lawyers and opposition party supporters had planned to gather near Lahore's main court complex before heading toward Islamabad to stage a mass sit-in protest in front of Parliament, in defiance of a government ban.
Authorities used lorries to block major roads into the city and riot police took up positions outside the railway station and government buildings.
Several thousand flag-waving demonstrators pushed past police barricades to reach the courts.
But, by evening, the mood was jubilant as police pulled back, and thousands of flag-waving supporters and cheering lawyers turned out to cheer Mr Sharif.
'People have responded very overwhelmingly to the call of the hour and I am thankful to the nation,' he said.
'This is a prelude to a revolution.'
The political turmoil began last month when the Supreme Court disqualified the Sharif brothers from elected office over past criminal convictions.
President Asif Ali Zardari compounded the crisis by dismissing the Sharifs' administration in Punjab, of which Lahore is the capital.
But on Saturday, after US Secretary of State Hillary Clinton spoke to both Mr Zardari and Nawaz Sharif by telephone, the government announced that it would appeal against the Supreme Court ruling in the coming days.
Suspected militants attacked a transport terminal in north-western Pakistan used to supply NATO troops in Afghanistan before dawn on Sunday and torched dozens of containers and military vehicles.