Tens of thousands of anti-government protesters gathered in Pakistan's capital late Friday in the pouring rain following the arrival of convoys led by a cricket star-turned-politician and a fiery, Canada-based anti-Taliban cleric.
The twin protests led by Imran Khan and cleric Tahir ul Qadri represent the biggest challenge yet to Pakistani Prime Minister Nawaz Sharif's year-old government and security had been tightened across Islamabad amid fears of unrest in a country with a long history of chaotic politics and military coups.
The protesters left the eastern city of Lahore on Thursday, vowing to march to the capital and camp out there until their demands for a new government are met.
Despite the darkness and the lashing rain, the crowds swelled as they entered Islamabad shortly before midnight.
Police estimated about 60,000 people were taking part in the protest. The protests were festive despite the rain, with demonstrators waving national and party flags and dancing to drum beats and patriotic songs.
As he approached the Islamabad airport, Mr. Khan tweeted that he would stage the sit-in on the city's main Kashmir Highway. "Sharif should have his resignation ready," he said.
A spokesman for Mr. Qadri, Shahid Mursaleen, said the cleric would deliver a speech on Saturday to call for Mr. Sharif's removal and immediate arrest.
Mr. Sharif says he is ready to meet with his opponents but has given no indication that he would step down. As his spokesman, Pervaiz Rashid, told a local news channel: "Pakistan is not a banana republic, where a few thousand people come and seek the resignation of the country's Prime Minister."
Thousands of riot police have been deployed across the capital. Authorities set up shipping containers to block traffic and cut off cellphone service in some areas.