Panama votes Sunday in a presidential election with the frontrunner's participation confirmed after a last-minute court decision validated his run against seven other contenders.

Conservative lawyer Jose Raul Mulino is far ahead in opinion polls with about 30 percent of voter intention, but was left waiting until Friday for the Central American country's Supreme Court to rule on whether he would be allowed to participate at all.

Mulino replaced ex-president Ricardo Martinelli as the candidate for the right-wing Realizing Goals (RM) party after Martinelli lost an appeal against a money laundering conviction.

Mulino's candidacy was challenged on the basis that he had not won a primary vote or picked a running mate, as required by law.

Mulino had been Martinelli's vice-presidential running mate until his disqualification.

The Supreme Court dismissed the complaint on Friday, with the body's president Maria Eugenia Lopez saying the judges were swayed by the right of Panamanians "to elect and be elected, and political pluralism."

There are seven other candidates -- of whom only three approach 15 percent support in a country battling deep-rooted corruption, a severe drought that has hobbled its economically critical Panama Canal, and a stream of US-bound migrants passing through its jungles.

Polls show there are more undecided voters than support for any of the seven.

Trailing Mulino are social democratic ex-president Martin Torrijos and two center-right politicians: Martinelli-era foreign minister Romulo Roux and Ricardo Lombana, a former envoy to the United States.

Lombana had placed a surprise third in Panama's 2019 presidential vote, behind Roux in second place.

Some three million of Panama's 4.4 million citizens are eligible to participate in Sunday's single-round vote, with a simple majority required for victory.

They will also elect a new National Assembly.

- 'Triumph of impunity' -

Before he could be arrested to serve his sentence, Martinelli found asylum with his dog Bruno at the Nicaraguan embassy in February.

Even in his absence, the ex-president has figured heavily in the campaign. He remains popular despite being found guilty of abusing stolen public money.

Many long for the days of economic prosperity under his government from 2009 to 2014, aided by an infrastructure boom that included the enlargement of the canal and construction of Central America's first metro line.

Polls show that voters' main concerns are the high cost of living, access to drinking water and insecurity.

"It's always the same: more corruption while people struggle because everything is more expensive," said 53-year-old homemaker Angela Justavino, who was unclear on who she would vote for.

Mulino, who had served as Martinelli's security minister, has dismissed the criminal case against his former boss as politically motivated.

"If Mulino wins, everything we have achieved in bringing high-profile corruption cases to court... will be erased," possibly through a pardon for Martinelli, Transparency International's Panama head Lina Vega told AFP.

"It will be the triumph of impunity."

- Economy, climate change -

President Laurentino Cortizo of the majority PRD center-left party will vacate his seat after a term marred by allegations of widespread official corruption, declining foreign investment and rising public debt.

Panama has a presidential one-term limit.

About 45 percent of jobs in Panama today are in the informal market, with unemployment nearing 10 percent.

A third of the rural population lives in poverty.

At the same time, the country's economic engine -- the Panama Canal that moves about six percent of global maritime trade -- has had to limit ship transit amid a crippling drought.

"The fiscal situation, the economic model... and the sustainability of the canal in the face of climate change" will be challenges for the new government, said political scientist Claire Nevache.

The Cortizo government also had to deal with widespread social unrest sparked by its decision to prolong the life of Central America's biggest open-pit copper mine -- granting a new licence to a Canadian company despite environmental concerns.

That project has since been scrapped, and the new president will have to face the dispute that has sparked with First Quantum Minerals.

Another headache awaiting the newcomer is the Darien Gap between Colombia and Panama through which more than half a million undocumented migrants passed last year, suffering abuses criticized by rights groups.

Mulino has vowed to close the gap.

Polls will open for eight hours from 07:00 am local time (1200 GMT) on Sunday.