By Mubasher BukhariLAHORE, Pakistan (Reuters) - Tens of millions of Pakistanis voted on Saturday in local government elections for the first time in ten years, polls seen as a referendum on the ruling party midway through its term.The opposition, led by international cricket star turned politician Imran Khan, is hoping to build a national coalition that could challenge Prime Minister Nawaz Sharif's Pakistan Muslim League-Nawaz (PMLN) partyat the next general election.Elections are being held in two of Pakistan's four provinces - the central province of Punjab and southern province of Sindh.Pakistan's other two provinces held local elections months ago. Khan won in Khyber Pakhtunkhwa in the northwest and Sharif's party and its coalition partners won in the sparsely populated western province of Baluchistan.Observers are closely watching the polls in Punjab, Pakistan's richest and most populous province and the power base of Sharif, who swept to national power in a landslide election in 2013."PMLN has the upper hand in Punjab but it will be a strongly challenged by PTI," said political analyst Wajahat Masood, referring to Khan's Pakistan Tehreek-i-Insaaf party.Security and theeconomyhave improved under Sharif but the government has failed to tackle corruption or tax dodging by the wealthy, two problems that are starving social services such as schools and hospitals of cash.Over 20 million people are registered to vote in Punjab and 4.6 million in Sindh. Pakistan has a population of 190 million.Local bodies, in which voters elect councillors directly, devolve administrative and financial powers to lower tiers of electoral bodies.Local government elections were last held in 2005 under General Pervez Musharraf, who came to power in a bloodless coup.National and provincial political parties dislike the system, saying the military has previously used it to undermine parliamentary democracy.In March this year, the Supreme Court called the absence of the local government system for over a decade unconstitutional and ordered the election commission to arrange for polls to be held as soon as possible.(Writing by Mehreen Zahra-Malik; Editing by Tom Heneghan)Join the conversation about this story Click here to read full news..