With former Prime Minister Nawaz Sharif in jail over corruption charges along with his daughter and son-in-law, the main contest will be between his demoralized Pakistan Muslim League-Nawaz (PML-N) and cricketer-turned-politician Imran Khan's PTI which critics say enjoys the backing of the military and the Inter-Services Intelligence (ISI).

Also in the fray are the Pakistan Peoples Party (PPP) of Asif Ali Zardari and Bilawal Bhutto and, ironically, Mumbai terror mastermind Hafiz Saeed's son Hafiz Talha Saeed and son-in-law Khalid Waleed. These two are among 260 candidates fielded under the umbrella of 'Allah-o-Akbar Tehreek', which was registered with the Election Commission in 2011.

The last democratically elected government completed its full term on May 31 but by then Pakistan was in turmoil, with Imran Khan, who is said to enjoy a lead in the election, launching a no-holds barred attack on Nawaz Sharif, who was forced to step down as Prime Minister by a court on corruption charges.

Political parties and their candidates made intense, last-minute efforts to garner support just before electioneering ended at midnight on Tuesday.

Polling will begin at 8 a.m. on Wednesday and end at 6 p.m. Over 100 political parties are in the fray for 272 seats in the National Assembly.

In all, 3,459 candidates will contest 272 seats. Another 60 seats are reserved for women while 10 have been kept aside for religious minorities including Hindus.

Around 1.6 million electoral staff will be on duty on polling day. Nearly half a million police personnel will be deployed, out of which 202,100 will be posted in Punjab and Islamabad and 100,500 in Sindh.

"The time has come for you to make this movement a success and announce such a historic verdict which may sweep away all those verdicts that have made Pakistan a graveyard of justice," said Sharif in an audio message from Adiala jail.

PML-N President and Sharif's younger brother Shehbaz Sharif asserted on Monday that the PML-N was set to win.

Imran Khan continued to be aggressive, telling huge rallies in PML-N stronghold Lahore on Monday night that the Sharif claims of development were "only in advertisements". He urged the people to change the fate of Pakistan.

According to an Election Commission official, 5,878 polling stations have been declared "highly sensitive" -- official euphemism to mean they are prone to violence -- in Sindh, 5,487 in Punjab and Islamabad, 3,874 in Khyber Pakhtunkhwa and FATA and 1,768 in Balochistan.

In a special message, Chief Election Commissioner Justice (retd) Sardar Raza Khan urged people to vote without fail. He promised a free and fair election.