Hundreds of people queued up at 43 polling stations in a constituency of Pakistan's port city of Karachi on Sunday where a re-vote had been ordered over allegations of ballot stuffing.
The re-poll of an eligible 86,000 voters in a constituency known as NA-250, largely an affluent neighbourhood, started at 8:00 am (0300 GMT) under tight security involving army, police and paramilitary rangers, an AFP reporter said.
The voting came a day after three gunmen on a motorbike killed Zohra Hussain, 59, vice president of the women's wing of Pakistan Tehreek-e-Insaf (PTI), in the province of Sindh, outside her home in an upmarket part of the city.
PTI chief and former cricket star Imran Khan blamed the Muttahida Qaumi Movement (MQM) party, which represents the Urdu-speaking majority, and specifically its boss, Altaf Hussain, who lives in exile in London.
Karachi was the focus for allegations of fraud during Pakistan's landmark general elections on May 11 that saw some 50 million Pakistanis vote, with centre-right former prime minister Nawaz Sharif emerging the winner nearly 14 years after he was deposed in a coup.
The MQM and Pakistan Peoples Party (PPP) had already announced they would boycott Sunday's vote after the election commission rejected their demands of a re-do for the entire constituency instead of just 43 polling stations.
"We want a change -- a real change in our country because we are fed up with the current political set up, which is just disappointing," housewife Arifa Aslam told AFP as she waited in a long queue at one station to cast her vote.
PTI's Arif Alvi, who is contesting the election for a national assembly seat from NA-250, was content with the heavy security presence.
"I am quite satisfied with the security arrangements. People are casting their vote without any fear as polling stations are well guarded by security forces," he told AFP.
The official partial results released Tuesday by the election commission gave Sharif's Pakistan Muslim League (N) 123 out of the 272 directly elected seats while the PPP suffered a crushing defeat, dropping from 95 seats to 31.
Khan's PTI moved into third place on 26 seats compared to none in the last assembly.