The polling began at 8 am and continued till 5 pm but in several districts.
Pakistan Tehreek-e-Insaf (PTI) has won the by-elections on Punjab Assembly seats which were held on Sunday.
Pakistan Muslim League-Nawaz (PML-N) has "conceded defeat and congratulated" its rival part on victory in "crucial by-elections on Punjab Assembly's 20 seats."
According to initial results on Sunday, PTI candidates secured victory in Multan, Dera Ghazi Khan, Sahiwal, and Khushab provincial assembly seats while the party took the lead by a clear majority in 15 constituencies of the province, The Express Tribune reported.
PML-N Vice-President Maryam Nawaz, who spearheaded her party's by-election campaign, said the ruling party should accept the election results with an open heart.
Maryam also called for carrying out introspection saying efforts should be made to identify and overcome shortcomings. "God willing, everything will be fine."
"PML-N should openly accept the results. One should bow before the decision of the people. In politics, there are always wins and losses. The heart should be enlarged. Wherever there are weaknesses, efforts should be made to identify them and overcome them. God willing, it will be fine," she tweeted.
Punjab was under the control of the PTI party until April when then-Chief Minister Sardar Usman Buzdar resigned after the federal parliament took up a no-confidence against Khan.
The PTI's subsequent nominee for the position was defeated as a faction among the party's state lawmakers voted for the PML-N's candidate instead.
Khan then successfully petitioned the Election Commission of Pakistan to remove the state assembly lawmakers for illegally voting against the party's directive, leaving 20 seats vacant.
The polling began at 8 am and continued till 5 pm but in several districts, polling was stopped due to clashes, reported Dunya News.
20 seats fell vacant after the Election Commission of Pakistan (ECP) "de-seated" 25 PTI dissident lawmakers on May 23 for voting against PML-N's Hamza Shahbaz in the Punjab chief minister's election.
By-elections were held in 20 constituencies of the Punjab Assembly including polling stations PP-7 Rawalpindi, PP-83 Khushab, PP-90 Bhakkar, PP-97 Faisalabad; PP-125, PP-127 Jhang, PP-140 Sheikhupura, PP-158, 167,168,170 Lahore; PP-167, Lahore, PP-202 Sahiwa; PP-217 Multan, PP-224 Lodhran, PP-228 Lodhran, PP-237 Bahawalnagar, PP-272,273 Muzaffargarh, PP-282 Layyah and PP-288 Dera Ghazi Khan.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)