The violence occurred in the Kahirpur district of the southern Sindh province - a political stronghold of the Pakistan People's Party (PPP), once headed by slain former prime minister Benazir Bhutto.

The local police said that dozens of people were also wounded in the clashes between the supporters of the PPP, which rules the Sindh province, and the Pakistan Muslim League (PML-F), headed by the South Asian country's famous spiritual leader Pir Pagara.

The two groups clashed an hour before the end of polling for the second round of local government elections on Saturday. The Khyber Pakhtunkhwa and Balochistan provinces held the vote a month ago.

"Eleven people were killed when two groups opened fire," police officer Kamran Fazal told the Reuters new agency.

The government has called in army troops to control the situation, local media reported.

Owais Tohid, a senior Pakistani journalist based in Islamabad, said the Khaipur district has had a history of political and sectarian turmoil. "It is the hometown of the incumbent head of the provincial government, Qaim Ali Shah, and at the same time there are a large number of Pagara disciples in the area. This, obviously, has led to a tug of war for the area's control," Tohid told DW, adding that hundreds of polling stations had been declared "sensitive" prior to Saturday's voting.

A test for PM Sharif's popularity

Cricketer-turned-politician Imran Khan has seriously challenged the popularity of Prime Minister Nawaz Sharif in the central Pujab province, which is also holding local elections in several phases. Khan's Pakistan Tehreek-e-Insaf (PTI) party lost to Sharif's Muslim League in the 2013 general elections, but Khan has been using street protests to oust the veteran politician from power since last year.

Khan led huge public rallies against PM Sharif last year

Experts say the local elections in Punjab could be a major political test for both Sharif and Khan.

"Sharif's party is likely to win the elections in Punjab, as it has a better organizational structure in the province than Khan's PTI, which is only relying on the charisma of its leader," Tohid underlined.

Political analysts Wajahat Masood agrees: "Sharif's party has the upper hand in Punjab but it will be strongly challenged by PTI," he told Reuters.

The PTI activists, however, complain that the vote is not being held in a fair manner and have reported electoral irregularities.

"The administration is supporting the ruling party's candidates. It is a violation of the rules set by the election commission," Bela Ahmed, a PTI supporter in the Rawalpindi city, told DW.

DW's correspondent in Lahore, Tanvir Shahzad, also reported clashes in various parts of the province.