Report says violence has erupted as millions head to the polls in Pakistan, with at least 31 dead in the worst attack, a bomb in the city of Quetta.
Voters are deciding between the parties of the former cricket star Imran Khan and the disgraced former Prime Minister Nawaz Sharif.
But the campaign has been overshadowed by concerns of fraud and violence.
The Human Rights Commission of Pakistan says there have been “blatant” attempts to manipulate the polls.
Mr Khan has vowed to tackle entrenched corruption but his rivals accuse him of benefitting from alleged meddling by the powerful military, which has ruled Pakistan for nearly half of its history.
Pakistan is no stranger to political turmoil and the last few months have proved no exception. Nawaz Sharif, the man who won the last election, is watching this contest from prison. He has been jailed for corruption after a scandal stemming from the Panama Papers leak.
Despite tight security across the country, with more than 370,000 troops and hundreds of thousands police officers deployed to secure the ballot, there have been incidents of violence.
Officials say the attack in Quetta, in Balochistan province, was the work of a suicide bomber targeting police at the gate of a polling station. The Islamic State (IS) group said it was behind the attack.
Pakistan has been ruled on and off by the military during its 71-year history. This election is significant because it will mark only the second time that one civilian government has handed power to another after serving a full term.
But the run-up to the vote has been controversial.
The Pakistan Muslim League-Nawaz (PML-N) complains of a targeted crackdown by the powerful security establishment, with the alleged help of the courts, in favour of Imran Khan and his Pakistan Tehreek-e-Insaf (PTI).
On Sunday, a judge in the High Court of Islamabad appeared to back up that allegation, saying that the military Inter-Services Intelligence (ISI) organisation had been interfering in the judiciary.