According to data available from the Election Commission of Pakistan's (ECP) newly-introduced Result Transmission System (RTS), PTI's Arbab Amir Ayub is leading the race for the NA-4 constituency in Peshawar with 43,812 votes.
He is followed by PML-N's Nasir Khan Musazai, who has received 23,827 votes so far; 23,428 votes had been polled in favour of ANP candidate Khushdil Khan.
Votes from 258 polling stations have been counted while votes from 11 polling stations have yet to be counted.
Celebratory gunfire has been reported outside PTI candidate Arbab Amir Ayub's house.
Polling for the crucial by-election had wrapped up without any major untoward incident earlier in the day.
Many observers consider the by-poll a litmus test for the popularity of the Pakistan Tehreek-i-Insaf (PTI) government in the province.
The seat had fallen vacant after the death of dissident PTI MNA Gulzar Khan on August 28. His son, Asad Gulzar, is now contesting the seat on a PPP ticket while his main opponents are Arbab Amir Ayub of PTI, Khushdil Khan of ANP and Nasir Khan Musazai of PML-N.