MULTAN, Pakistan (AFP) - Gunmen on Thursday kidnapped the son of a former Pakistani prime minister on the last day of campaigning for elections and shot dead one of the son's aides, police said.

Mr Ali Haider Gilani, a candidate for the Punjab provincial assembly, was seized in a hail of gunfire on the outskirts of the city of Multan in the province.

Former prime minister Yousuf Raza Gilani and his kin are one of the most powerful families in the area.

"People came on a motorbike. They also had a car with them and they opened fire and abducted Yousuf Raza Gilani's son Ali Haider in a black Honda," police officer Khurram Shakur told reporters.

"We have closed the entry-exit points and launched a search," he said.

Another police officer told AFP that one of Mr Haider's staff members had been killed.

"Ali Haider's secretary Ghulam Mohiuddin was killed in the firing," said local police official Abdul Qayyum, adding that five other people including one of Mr Haider's guards were injured.

The incident happened in the Matital area on the last day of official campaigning for Saturday's election, which will mark a landmark democratic transition in a country that has been ruled for half its life by the military.

Provincial elections are also being held and Mr Ali Haider is a provincial assembly candidate for the secular Pakistan People's Party (PPP). He has two other brothers standing for the national assembly.

Mr Gilani senior was disqualified after being sacked and indicted by the Supreme Court last year for refusing to reopen corruption cases against the president.

His elder son Ali Musa spoke to reporters in tears after the abduction.

"We want our brother back tonight. If we don't get him, we will not allow elections to be held in our area," he said.

The PPP has led the national government for the last five years but has run a lacklustre campaign, with its chairman, Bilawal Bhutto Zardari, too young to contest the vote and kept out of public view due to Taleban threats.