A bomb attack killed at least 31 people and injured more than 30 others Wednesday as Pakistanis voted amid heavy security in a fiercely contested general election.
The explosion took place on the outskirts of Quetta, capital of Balochistan province. The cause of the blast was unknown, said the city's police superintendent, Naseeb Ullah.
Sardar Mohammed Raza, the chief election commissioner, strongly condemned the attack, offering condolences to grieving families and demanding a report on "improper security arrangements."
Shopkeeper Akber Khan, who witnessed the attack, said he had already cast his vote at a nearby polling station and returned to his shop. Stepping outside again, he'd "hardly walked a step or two" when the blast occurred.
"We got down on the ground. Most people started running. After 10 minutes, when the chaos was over, we started picking up the injured. We carried them into private vehicles as ambulances had not arrived yet."
ISIS has claimed responsibility for the attack. CNN cannot independently verify this assertion.
Meanwhile in Khyber Pakhtunkhwa in northwestern Pakistan, one person was killed and three injured in a skirmish outside a polling station between supporters of Imran Khan's Pakistan Tehreek-e-Insaf and the province's Awami National Party.
Khan condemned the Quetta blast, saying in a tweet he was "saddened by the loss of innocent lives" and that "enemies of (Pakistan are) seeking to disrupt our democratic process. ... Pakistanis must defeat the terrorists' design by coming out in strength to cast their vote."
The tightly fought race pits the party of the former cricket star against that of jailed former premier Nawaz Sharif.
Shahbaz Sharif, who replaced his brother as their party's candidate, said in tweet: "Heartbroken to learn of martyrdom of innocent people including police officials. ... My profound condolences to the bereaved families."
A huge security operation was launched after attacks in the lead-up to the election. On July 16, a suicide bombing targeting a candidate killed 150 people in Balochistan and led to suggestions the vote should be delayed.
Police and military personnel were out in force at polling stations across the country, with security officials flying surveillance drones in the troubled northwest city of Peshawar. There were long lines of voters in the major cities of Karachi, Quetta and Peshawar.
Two parties, the incumbent Pakistan Muslim League-Nawaz and the Pakistan People's Party, that of former Prime Minister Benazir Bhutto, formally asked for an extension in voting hours, but the electoral commission denied the request.
Army officials said more than 370,000 troops had been deployed to ensure a "fair and free" election, with police estimating the total security force at 800,000 personnel.
8 a.m. local (11 p.m. ET Tuesday): Polls opened.
6 p.m. (9 a.m. ET): Polls closed.
8 to 9 p.m. (11 a.m. to noon ET): Election Commission of Pakistan to begin announcing regional results.
11 p.m. onward (2 p.m. ET): General results should start coming in; candidates may begin conceding or declaring victory.
Wednesday's headlines were dominated by the pivotal election, with one newspaper describing it as on a "knife-edge." Many also noted the heavy security presence as voters went to the polls.
Nearly 106 million people are registered to vote for members of the lower house of Parliament and four provincial assemblies.
This week's election is only the second time in Pakistan's 71-year history that the country has seen a democratic transition of power.
The run-up to the vote has been dogged by increasing tensions over allegations that the powerful military has secretly backed Khan, a massive crackdown on the media and the electoral participation of militant groups.
The Human Rights Commission of Pakistan has expressed "serious reservations about the extraordinary powers accorded to security forces" and called the election "the dirtiest" in the country's history.
After polls closed Wednesday, military spokesman Maj. Gen. Asif Ghafoor thanked Pakistanis for proving their "love & respect" for the armed forces and other law enforcement by going to the polls.
You have "rejected all kinds of malicious propaganda. We are strong because we have your unflinching support," he tweeted in a veiled reference to allegations of military interference.
Khan has repeatedly denied accusations he is supported by the military and condemned the harassment of election candidates.
The former Pakistan cricket captain said he had voted, telling reporters: "I am a sportsman; I'm not going to declare victory until the last bowl has been bowled."
With the incumbent Pakistan Muslim League-Nawaz still on the back foot after Nawaz Sharif's imprisonment, the election represents a real chance for Khan's center-right Pakistan Tehreek-e-Insaf, or PTI, to break into the two-party system that has traditionally dominated national politics.
The final result may go down to the wire, however, leaving candidates in coalition negotiations, either with the once-dominant Pakistan People's Party -- led by the 29-year-old Bilawal Bhutto Zardari, son of former President Asif Ali Zardari and Benazir Bhutto -- or with some of the wide array of smaller parties.
These parties, including some religious groups, could assume a new level of importance if Khan or another candidate need to rely on them to form a coalition government. Far-right Islamist parties are among these fringe groups, including some known to be sympathetic to militants.
Khan has built on his sports celebrity and the PTI's success as a regional party to emerge as a change candidate, attracting religious conservatives and drilling down on Pakistan's endemic corruption -- a task made easier by Sharif's conviction.
Some analysts, however, say that Khan lacks national-level political experience to enact any meaningful reform and will be hampered by less-than-loyal allies in his party and the influence of the military.
Khan's supporters remain optimistic that if elected, his slogan of building a "New Pakistan" would bear fruit.
"I have just voted for PTI," said Amna Gardar in Lahore, capital of Punjab province. "If you want to be part of that change, please come out, please vote."
All eyes will be on whether Shahbaz Sharif can maintain the Pakistan Muslim League-Nawaz's grip on its stronghold in Punjab, Pakistan's most populous and richest province. It will be difficult for Khan to take power without winning Punjab. Analysts were divided over whether Nawaz Sharif's jailing would generate a sympathy vote.
Whoever forms the next government of Pakistan, an Islamic republic of 207 million people, will have to deal with a massive debt crisis. The nuclear-armed state also faces uncertainty over its relationships with the United States, which has cut military aid due to Islamabad's alleged support for the Taliban in neighboring Afghanistan, and China, which has financed multibillion-dollar infrastructure projects in the South Asian country.