Guatemalans are casting ballots in a presidential runoff, choosing between a comedian with no political experience and a former first lady, amid the fallout of a massive corruption scandal.

Jimmy Morales, a comic actor, headed into the vote with a huge lead - 68 percent to 32 percent for former first lady Sandra Torres, according to the final opinion poll.

It has been a remarkable ride for the conservative candidate, who started the race with just 0.5 percent support back in April.

Comedian Jimmy Morales is running for president with the National Front of Convergence party [AP]
His surge has capped a tumultuous campaign rocked by president Otto Perez's resignation and arrest on corruption charges on September 3, three days before the first round of voting.

An estimated 7.5 million people are eligible to vote in the second round.

Whoever wins must rebuild confidence in government at a time of deep public distrust, shaky institutions and a depleted treasury.

"The new president will face a sombre panorama because the state is in a death spiral," Manfredo Marroquin, head of the local chapter of Transparency International, told the AFP news agency.

If Morales wins, he will have to govern with just 11 seats in the 158-seat Congress.

Former first lady Sandra Torres is running for president with the National Unity of Hope party [AP]

Perez, who is in jail awaiting trial, is accused of masterminding a corrupt network of politicians and customs officials that allowed businesses to pay bribes to get illegal discounts on import duties.

Prosecutors and United Nations investigators say the network collected $3.8m in bribes between May 2014 and April 2015 - including $800,000 each to Perez and jailed ex-vice president Roxana Baldetti.

The scandal, the worst in a string of recent corruption cases, has created an unprecedented climate of outrage in Guatemala, an impoverished Central American country torn by gang violence and still recovering from a 36-year civil war that ended in 1996.

Thousands of protesters, including from the country's large and historically marginalised indigenous population, took to the streets in the weeks leading up to the elections, pressing an ultimately successful campaign for Perez to quit.

Source: Agencies