Police in Manila say at least 30,000 people have rallied in the city's business district to call for Philippine President Gloria Arroyo's resignation.
Organizers had hoped for a turnout of about 40,000-to-50,000 people Wednesday as a concrete sign of disgust with Mrs. Arroyo, who has been accused of rigging the vote in the May 2004 presidential election.
Mrs. Arroyo has rejected a chorus of calls for her to step down, including a plea from former President Corazon Aquino.
Philippine soldiers and police have been placed on high alert against possible terrorist attacks during the demonstration.
The ongoing political crisis has taken a toll on the Philippine's economy. A third major rating agency (Moody's Investor Service) downgraded its economic outlook to negative earlier Wednesday.
Some information for this report provided by AP, AFP and Reuters.