BENIGNO Aquino, the front-runner in the race to succeed Philippines President Gloria Arroyo, formally registered his candidacy in the May 2010 election yesterday with a pledge to fight corruption, witnesses said.

Aquino, a senator and the son of the late president Corazon Aquino, filed his registration papers at the Commission on Elections office here.

More than a thousand supporters, like him clad in yellow, held a festive rally outside, an AFP photographer saw.

Aquino, 51, wants to effect "transformational change" after nine years of rule by Arroyo, an estranged former political ally of his family.

"Its legitimacy is under question. It persecutes those who expose the truth about its legitimacy and corruption.

It stays in power by corrupting individuals and institutions," his Liberal Party alleged in paid advertisements on national newspapers yesterday.

His main rivals for the presidency, Arroyo's preferred successor and ex-defence secretary Gilberto Teodoro, multi-millionaire developer and senator Manny Villar, and deposed former president Joseph Estrada are all expected to register before the deadline on Monday.