The Southeast Asian nation's chaotic brand of democracy will see 50 million voters choose a new president and thousands of lower positions on May 10, but observers warned candidates' promises of change were likely to prove hollow.

"I don't think there will be any change in the idiosyncrasies that define the Philippines," Robert Broadfoot, managing director of the Hong Kong-based Political and Economic Risk Consultancy group, told Agence France-Presse.

The official start of the election season on Tuesday allowed the presidential candidates to hold rallies and appeal directly to people for their votes, while spending limits on advertising took effect.

One of the frontrunners in the presidential contest is Senator Benigno "Noynoy" Aquino III, who spectacularly rode into contention last year on a wave of sympathy following the death of his mother, democracy heroine Corazon Aquino.

However his huge lead in surveys has eroded almost as quickly as it was gained, with mega-rich property developer Senator Manuel Villar having caught him with nearly 40 percent support in surveys following an advertising spending spree.

Adding spice to the presidential race is deposed former president Joseph Estrada's attempt at political resurrection, after he was deposed halfway through his first term in 2001 and later convicted of corruption.

Estrada is running third in the surveys and, although an outside chance, analysts said the former B-grade movie star could yet achieve his wish of redemption.

"It's going to be difficult for him, but he has 100 percent name recognition across the country—it depends on how diligently he runs his campaign," said Ronald Holmes, a political lecturer at De La Salle University in Manila.

The ruling coalition's choice to succeed President Gloria Macapagal-Arroyo, former defense secretary Gilberto Teodoro, is running a distant fourth with just five percent support in the latest surveys.

However Holmes, also president of polling firm Pulse Asia, said picking a winner three months from the election was impossible, and even Teodoro had a chance if the coalition's formidable machinery could kick into action.

For an international audience, much interest will focus on Manny Pacquiao, the seven-time world champion boxer who is running for a seat in the House of Representatives.

Pacquiao is counting on his hero status across the country to get him elected, but he failed in a similar bid in the 2007 congressional elections and Holmes said could again be struck a knock-out political blow.

"It's going to be difficult for him. He is up against someone who has been in local politics for a long time," Holmes said.

Also seeking a lower house seat is Imelda Marcos, the 80-year-old wife of former dictator Ferdinand Marcos, whose rule ended in 1986 with the people power revolution led by former president Corazon Aquino.

Imelda is regarded as a near certainty to win the seat in the northern province of Ilocos Norte that is being vacated by her son, Ferdinand Marcos Jr., as the family has maintained its grip on power there for decades.

Meanwhile, President Arroyo, who is not allowed under the Constitution to seek re-election, has controversially registered to run for a House seat in her home province of Pampanga.

Arroyo's critics have warned she may secretly be aiming to use a congressional position as a power base to change the Charter and allow her to return to power as the country's first prime minister.

While the presidential candidates' election season began on Tuesday, those vying for lower positions will not be allowed to officially begin campaigning until March 26.