Express Tribune, quoting police in Multan in Punjab province, reported gunmen abducted Ali Haider Gilani, the youngest son of former Prime Minister Syed Yousuf Raza Gilani, as he was addressing Pakistan People's Party rally.
The report said the attackers arrived in two cars and opened fire at the gathering in Multan's Farrukh Town from where the younger Gilani is running in Saturday's general elections.
Ali Haider Gilani's personal secretary was killed in the attack and eight other people were wounded, the report said.
Police officials told the Tribune the target of the attack may have been the former prime minister, who apparently wasn't hurt.
"It is definitely an act of terrorists," the Tribune quoted a police official as saying.
Pakistan, with elections round the corner, has been plagued by violence in recent days in which several people have died. Gilani's party, leading the coalition civilian government, completed its five-year term in March, the first such government to do so in the country that has been intermittently ruled for decades by its powerful military.
Saturday's elections would mark the first democratic transition of power.
Witnesses told the Tribune the attackers dragged Gilani into a car before escaping.
Ali Musa Gilani, an older brother of Ali Haider Gilano, said party members weren't carrying weapons and didn't keep guards to comply with the election commission's code of conduct, the Tribune said.
"There was no security, no weapons. They [gunmen] came and easily took him away," he said.
There was no immediate claim of responsibility. However, the Tehreek-i-Taliban Pakistan, which has claimed responsibility for some of the other election-related acts of violence, has threatened to attack the PPP, the Muttahida Qaumi Movement and the Awami National Party and other secular parties.
Dawn newspaper said Multan police have launched a hunt for the kidnappers.