As votes were being counted in Pakistan's historic election, former Prime Minister Nawaz Sharif claimed victory and media projections put his Muslim League party ahead.
The vote marks Pakistan's first transition from one civilian government to another in its 66-year history.
The turnout was huge but the poll was marred by violence, the BBC reports.
In the worst election-day attack, 11 people were killed in the bombing of a political office in the biggest city Karachi.
Pakistan's election commission said it had been unable to carry out free and fair polls in the city and that voting would be re-run in some districts.
Voting was extended for an hour across the country before closing at 6pm. Counting was under way on Saturday in some areas.
But polls had been expected to remain open for three hours in seven constituencies in Karachi where voting was delayed because ballot boxes and papers had not arrived on time.
No official results have yet been released, but unofficial partial results suggested that Mr Sharif's party was ahead in more than 100 of the 272 directly elected parliamentary seats.
However, it is not clear if they will be able to win a simple majority of 136 seats.
In a speech at his party headquarters in the north-eastern city of Lahore, Mr Sharif said that the Muslim League (PML-N) was sure to emerge as the largest party.
The Movement of Justice (PTI) party of former cricketer Imran Khan has also performed well, with projections saying he had won a big victory in Peshawar. Mr Khan has continued to recover from a fall at an election rally.
President Asif Ali Zardari's Pakistan People's Party (PPP) is in a race for second place with the PTI, but both seem likely to win less than 40 seats.
Turnout is believed to have been high. An election commission spokesman said they hoped for a figure of 60-80%, compared to turnout in 2008 of 44%.