A blast has killed at least 20 people in Pakistan’s western city of Quetta on Wednesday in an attack targeting a police van, as the South Asian nation holds general elections.

Geo TV initially put the death toll at 18, while rival Samaa TV put it at 20, adding a “suicide attacker” was responsible.

Sky News reported later that a hospital official says 25 people have been killed and 40 wounded following the explosion outside a crowded polling station on election day.

Quetta: blast notification near polling station at east bypass.

Yah allah protect the people of pakistan 😢😢 pic.twitter.com/rHvkANsHNQ

— Bilal (@TheRonaldo7Way) July 25, 2018

Quetta is the capital of Pakistan’s province of Baluchistan.

Pakistanis began voting in a knife-edge general election pitting cricket hero Imran Khan against the party of jailed ex-Prime Minister Nawaz Sharif, with the prospect of neither winning a clear majority amid a looming currency crisis.

A decade after Pakistan was last ruled by a military government, the election has been plagued by allegations the powerful armed forces have been trying to tilt the race in Khan’s favour after falling out with the outgoing ruling party of Sharif, who was jailed on corruption charges this month.

Khan has emerged as a slight favourite in national polls, but the divisive race is likely to come down to Punjab, the country’s most populous province, where Sharif’s party has clung to its lead in recent surveys.

About 106 million people are registered to vote in polls due to close at 6pm (local time) on Wednesday. Results will start trickling in within hours.

Former cricketer Imran Khan is fronting an anti-corruption campaign. Photo: Getty

Whichever party wins, it will face a mounting and urgent in-tray, from the economic crisis to worsening relations with on-off ally the United States to deepening cross-country water shortages.

An anti-corruption crusader, Khan has promised an “Islamic welfare state” and cast his populist campaign as a battle to topple a predatory political elite hindering development in the impoverished mostly-Muslim nation of 208 million people, where the illiteracy rate hovers above 40 per cent.

Khan’s Pakistan Tehreek-e-Insaf (PTI) party has inched ahead of PML-N in recent national polls, but even if it gets the most votes, it will likely struggle to win a majority of the 272 elected seats in the National Assembly, raising the prospect of weeks of haggling to form a messy coalition government.

Such a delay could further imperil Pakistan’s economy, with the currency crisis expected to force the new government to turn to the International Monetary Fund for Pakistan’s second bailout since 2013. PTI has not ruled out seeking succour from China, Islamabad’s closest ally.

-with agencies