Fire gutted an election commission building in Manila early Sunday, destroying documents and guns for security officers, but crucial Philippine polls in May will go ahead, an official said.

No one was hurt in the pre-dawn blaze that hit the old, two-story building, which housed the election commission's headquarters before key offices were moved to a nearby building a few years ago.

The four-hour blaze destroyed documents that wouldn't affect the May 14 polls, along with weapons and ammunition also stored there, Elections Chairman Benjamin Abalos told reporters.

"It will be business as usual on Monday," Abalos said.

The lost documents related to the 2004 presidential and senatorial elections, he said.

Investigators said they were not ruling out arson, but have yet to determine the cause of the blaze.

Marines guarding the building, located in Manila's historic Intramuros district, would be asked why they did not immediately call firefighters when the fire started, Manila fire marshal Senior Superintendent Pablito Cordeta said.

The guards would also be questioned on why they were difficult to find at the height of the blaze, said Cordeta.

All 265 House of Representatives seats, half of the 24 Senate seats, and more than 17,500 local positions will be contested in the May 14 elections - considered crucial because the opposition could impeach President Gloria Macapagal Arroyo if it wins enough House seats.

Two opposition attempts to impeach Arroyo failed after her House allies, who hold the majority, blocked vote-rigging and corruption complaints filed against her.