Manila: The Philippine election season kicked into top gear on Friday as thousands of candidates hit the campaign hustings amid assassination fears, coup rumours and other claims of political skullduggery.

In one of Asia's most vibrant democracies, the polls on May 10 also offered hope for change following nine years of rule under President Gloria Arroyo that have been marred by allegations of corruption and vote cheating.

Benigno Aquino, the son of democracy heroine Corazon Aquino, is leading the presidential race as many voters embrace his promise of a cleaner government, with millionaire property developer Manny Villar running second in surveys.

Adding to the drama and colour of the election season, global boxing superstar Manny Pacquiao, former first lady Imelda Marcos and even Arroyo herself are running for seats in the House of Representatives.

But one of the over-riding themes is set to be the likelihood of candidates being shot dead before polling day, with dozens of people already having been killed in election-linked violence in recent months.

"We have long anticipated election-related violent incidents will go up during the campaign period on the local level," said national police spokesman Chief Superintendent Leonardo Espina."Historically, that is when the violence goes up."

While the presidential candidates have been campaigning since early February, the nearly 18,000 politicians vying for lower positions were only allowed to officially start canvassing for votes on Friday.

It is in these contests for positions such as governor, mayor or even town councillor that the rivalries are the most heated, officials warned.

In the most shocking case yet, 57 people including a candidate's wife and relatives as well as accompanying journalists were massacred in November allegedly by the private army of a powerful political clan.

The killings were allegedly carried out to keep the candidate from running against a clan member for the post of governor in the impoverished, strife-torn southern province of Maguindanao.

Elsewhere, at least 20 candidates have been killed and 13 others wounded in the run-up to the polls, Espina said on Thursday.

Fuelling the violence, there are up to 68 private armies of politicians still operating across the country that are defying a government order to put down their arms, according to election commissioner Rene Sarmiento.

There are also fears of illegal power grabs at the highest level.