LAHORE (AFP) - Pakistan's main parties on Wednesday suspended campaigning for weekend polls in honour of politician Imran Khan, who was in hospital with head and back injuries after falling at an election rally.

Television footage showed the retired cricket star and head of the Pakistan Movement for Justice party (PTI) flat on his back in a hospital bed, wearing a neck brace, looking pale and groggy after his fall in the city of Lahore.

Doctors have advised one week's rest, throwing the rest of his campaign for Saturday's election into jeopardy, but say his injuries are not life-threatening.

A televised statement that Mr Khan gave from his bed overnight, urging people to vote for his party, has since been re-released as a "paid content" advertisement for his PTI party, seeking to tap into a sympathy vote.

"I did whatever I could for this country. Now remember 11th May, come out and vote for PTI without considering its candidates, just vote for PTI," the 60-year-old said in a weak voice.

Hospital spokesman Khawaja Nazir told AFP that Mr Khan had one main head injury, two "fractures" to his back and a small injury to his shoulder.

"There is nothing serious to his injuries. He is in a private room, he is not in the ICU (intensive care unit). He has been shifted from the ICU to a private room," Mr Nazir told AFP.

Doctors are expected to provide a further update on his condition later on Wednesday, but Mr Nazir said that he has been "initially advised one week rest".

Mr Shafqat Mehmood, a spokesman for Mr Khan's PTI party, acknowledged that the injuries could stop Mr Khan appearing at any further election rallies.

"It is clear that general campaign will continue, but Imran Khan may not appear in the rallies now, we will have to see the doctors' advice," he said.

Mr Mehmood told AFP that other men who fell from the lift with Mr Khan were "fine" and were back home with their families with only minor injuries.

Mr Khan, who won only one seat in 2002 and boycotted polls in 2008, has led an electric campaign, galvanising the middle class and young people in what he has called a "tsunami" of support that will propel him into office.

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

Mr Khan's main rival, former prime minister Nawaz Sharif, who is tipped to win the election, called off campaigning on Wednesday and conveyed his sympathies.

"Nawaz Sharif decided to suspend all his election campaign-related engagements scheduled for today," PML-N spokesman Siddiqul Farooq told AFP.

"Sharif had plans to address several rallies in Punjab but they have been cancelled now. We have not given any advertisements against PTI, we are running a positive campaign," he added.

The Muttahida Qaumi Movement (MQM), which controls Pakistan's biggest city of Karachi, also announced on Twitter its leader Altaf Hussain, who is in self-exile in London, would not address supporters by telephone due to Mr Khan's condition.

Mr Khan's 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 111 people since mid-April, according to an AFP tally.

The Pakistani Taleban have condemned the polls as un-Islamic and directly threatened the outgoing ruling party, the secular Pakistan People's Party (PPP), and its main coalition partners, the MQM and the Awami National Party.

On Wednesday, a suicide bomber killed two people and wounded 23 others outside a police station in the northwestern district of Bannu, police said.

A female civilian and a policeman were killed when the suicide car bomber crashed into a barrier outside the station, local police chief Abdul Ghafoor Afridi told AFP.