Martin Romualdez, a cousin of President Ferdinand Marcos, told lawmakers he was leaving the post with a "clear conscience" so that a newly established investigatory body could do its job without "undue influence".

Public anger over so-called ghost infrastructure projects has been intensifying since Marcos put them centre stage in a July state of the nation address that followed weeks of deadly flooding.

Thousands are expected to turn out in the capital Manila on Sunday for a "Trillion Peso March", named for a Greenpeace estimate of $17.6 billion in funds allegedly bilked from climate-related projects since 2023.

"The issues surrounding certain infrastructure projects have raised questions that weigh not only upon me, but upon this institution we all serve," Romualdez said Wednesday at the House of Representatives.

"The longer I stay, the heavier that burden grows," he said, before formally tendering his resignation.

Barely an hour later, Faustino Dy, a longtime Marcos ally with a relatively low political profile, was elected as the new House speaker without opposition.

Last week, the owners of a construction firm accused nearly 30 House members and Department of Public Works and Highways officials of taking cash payments.

Romualdez was mentioned at the hearing as someone who had approved funding that did not require House oversight.

In a morning interview with local radio, Congressman Ronaldo Puno said Romualdez had told lawmakers the controversy was "too much" and that he planned to "step aside to face these allegations".

President Marcos on Monday announced former Supreme Court justice Andres Reyes would head a three-person commission tasked with looking into the past 10 years of flood control projects.

The Philippines has a long history of scandals involving public funds, in which high-ranking politicians found guilty of corruption have typically escaped serious jail time.

Senate president Francis Escudero was replaced by Vicente Sotto III early last week amid ongoing investigations by both houses of Congress into the flood control scandal.

Escudero's name was linked to one of the country's top flood control project contractors, a revelation he called a "demolition job" aimed at removing him from the Senate's top post.