Supporters of Pakistan Muslim League (PML-N) took to the streets in a protest rally on Friday, asking President Asif Ali Zardari to step down.
PML-N was expected to draw large crowds at the rally in its political heartland, Lahore.
Party supporters have been called to denounce government corruption, widespread power cuts, inflation and the poor standing of living, demanding early elections.
As the crowd gathered force, groups of PML-N followers danced to a drum as party singers praising leader Nawaz Sharif were blasted out at top volume.
Participants were served free drinks as slogans of “Go Zardari, go” echoed everywhere. “The time has come to shunt out Zardari,” activists shouted.
Lahore, with a population of eight million, is Pakistan’s second biggest city and the capital of the most populous province Punjab, which commands the greatest number of seats in the national parliament.
That makes it bitterly contested territory where opposition leaders are targeting the unpopular Zardari and trying to whip up votes for the future.
An AFP reporter said several thousand people swarmed along a wide, mile-long avenue, where participants were asked to text their names and constituency to Nawaz Sharif on a special number.
Demonstrators were frisked while armed policemen guarded the venue, where a large stage had been set up with bulletproof glass next to hoardings of Nawaz and his brother Shahbaz, chief minister of Punjab.
Police commandos were seen on the rooftops of buildings and Lahore police chief Malik Ahmed Raza Tahir told AFP that his officers were on high alert to prevent any possible attack by Islamist militants.
Members of Zardari’s main ruling Pakistan People’s Party (PPP) have lashed out at the Sharifs, accusing them of misappropriating Punjab resources.
“They are using government resources and functionaries for their political show,” Raja Riaz, who served as senior minister under Sharif when the PPP was briefly in the provincial ruling coalition, told AFP.
An irritant for Sharif and Zardari is cricket hero turned politician, Imran Khan, holding his own rally on Sunday at the Minar-e-Pakistan ground where the resolution for the creation of Pakistan was adopted on March 23, 1940.
Campaigning by his Tehreek-e-Insaf (Movement for Justice) party, which boycotted the 2008 election, has sparked debate about the extent to which he will deprive the Sharifs of support.