Benigno Aquino III told thousands of people he would deliver on his promise to tackle corruption when he was sworn in as the Philippines' 15th president today.

In his first speech as president, Mr Aquino said he would improve the investment environment and would sincerely seek a just resolution to a long-running Muslim separatist insurgency in the south.

‘My parents sought nothing less, and died for nothing less, than democracy, peace and prosperity,’ Mr Aquino told a crowd that police estimated at about 500,000 people.

‘I am blessed by this legacy. I shall carry the torch forward,’ he said at the ceremony at the Quirino Grandstand near Manila Bay.

Ahead of his inauguration, Mr Aquino met outgoing president Gloria Macapagal Arroyo at the Malacanang presidential palace, and the two travelled together to the grandstand.

Ms Arroyo did not stay for Mr Aquino's inauguration, which was watched by former presidents Joseph Estrada and Fidel Ramos.

On Tuesday, Mr Aquino said he was setting up a ‘Truth Commission’ to investigate allegations of corruption, electoral fraud and rights abuses against Ms Arroyo, who denies any wrongdoing, and her administration.

Ms Arroyo is not departing the political scene.

She won a seat in the lower house of Congress in the May election and could potentially block some of the new president's agenda.