Doctors said Wednesday they expect Pakistani politician Imran Khan to make a full recovery despite fracturing his spine at a campaign rally, as his party sought to capitalise on a sympathy vote.

The retired cricket star and head of the Pakistan Movement for Justice (PTI) suffered several fractured vertebrae and a broken rib on Tuesday when he fell from a lift raising him onto the stage at a rally in the city of Lahore.

Medical staff have ordered the 60-year-old to remain immobile in bed, throwing into doubt the prospect that he will address in person a final rally set to wrap up his high-octane campaign for office in Saturday's election.

The man tipped to win the polls, former prime minister Nawaz Sharif, suspended campaigning on Wednesday in tribute to Khan.

His fall was the latest dramatic twist to an election campaign that has been overshadowed by a series of attacks on politicians and political parties which have killed 113 people since mid-April, according to an AFP tally.

The Pakistani Taliban have condemned the polls as un-Islamic and directly threatened the outgoing secular Pakistan People's Party and its main coalition partners, the Muttahida Qaumi Movement and the Awami National Party.

On Wednesday a bomb targeted a candidate from the Awami National Party (ANP), killing two people and wounding three others in the northwestern tribal district of Bajaur, a local official said.

In another attack, unconnected to the elections, a suicide bomber killed three people and wounded 23 outside a police station in the northwestern district of Bannu, police said.

Aides said Khan would still address a final election rally on Thursday, even if it has to be from hospital.

Television footage showed him flat on his back in hospital wearing a neck brace, and looking pale and groggy after his fall in the city of Lahore.

Doctors have advised at least two days' rest but say he is in full control of his limbs and bodily functions and expected to make a full recovery.

A television statement filmed from his bed in which Khan urged people to vote for his party has been re-released as a "paid content" advertisement for PTI.

"Mr Khan has been advised bed rest for the next one or two days and after that doctors will review his condition and decide accordingly," Doctor Faisal Sultan, the head of the private Shaukat Khanum hospital, told reporters.

"The exact duration of how long he will require bed rest or immobilisation will be decided as time goes on."

A medical report listed a series of fractures to Khan's spine, one in his neck, another in a rib and an injury to his scalp.

But Sultan stressed that Khan's spinal canal was intact and "he is in total control of all limbs and body functions".

Party official Shah Mehmood Qureshi said PTI's campaign finale -- a rally outside parliament in Islamabad -- would go ahead as planned on Thursday evening.

"Wherever he is, in any condition, even from the ICU (intensive care unit), he will address the nation in the last moments of the campaign," Qureshi said.

Saturday's vote will be a democratic milestone in a country ruled for half its history by the military. It will be the first time a civilian government has served a full term and handed over to another through the ballot box.

It remains unclear whether a wave of sympathy for Khan will improve his poll prospects. Most commentators expect him to do well enough to become a strong opposition but not to form a government.

Khan, who has only ever won one seat, led an electrifying campaign until his fall, galvanising the middle class and young people in what he has called a "tsunami" of support that will propel him into office.

"Definitely in Pakistan people get very sympathetic when things like this happen. We expect to see a five to 10 percent increase in our support at least," said Salman Malik, a PTI worker campaigning in the Punjab town of Narowal.

Haseeb Asif, 27, a writer speaking to AFP in the same town, said Khan's fall had not swayed his own vote but predicted it might do so that others.

"The fact that Imran Khan had a primetime speech from his bedside, that's very powerful," he said. "I wasn't voting for PTI before. I haven't changed my mind but I can see how other people would."

Sharif, a millionaire steel tycoon, won praise for suspending his campaign and joining other political leaders to convey his sympathies.