The government has warned of possible attacks by armed groups over the election period, including attacks by fighters from New People's Army which, the authorities say, could launch attacks in 14 provinces across the country.
Oscar Calderon, the national police chief, said he had ordered police commanders nationwide to take steps to pre-empt "the hostile plan of the communist terrorists".
The elections are for 12 out of 24 senators and all 236 members of the House of Representatives.
More than 17,000 local officials, including governors and mayors will also be elected. Vote counting is done by hand, so final results will not be expected for weeks.
Arroyo's presidency, though, is not at stake, although analysts have said the result could have a bearing on the opposition's efforts to unseat her over allegations that she cheated to win the May 2004 ballot, allegations she denies.
But opinion polls suggest that no major shifts are likely. The economy in what is one of Asia's poorest countries has been rallying, with the stock market up 12 per cent this year and the peso at its strongest level against the US dollar since October 2000.
The deaths of hundreds of activists and supporters of opposition parties, killed since Arroyo came to power in 2001 with many alleged to have been victims of extrajudicial killings by the military, have led to greater international scrutiny of the country's elections.
|Candidates campaigned over |
a three-month period [AFP]
Police have put the official toll from the three-month campaign period at 113.
Military units have been drafted in to transport ballot boxes and escort foreign observers to outlying areas of the archipelago.
Aside from foreign observers accredited by the government, an independent team of 25 from 10 countries said they would monitor 13 areas that have been hit by violence and allegations of fraud.
The team comprises journalists, academics and others from countries including Japan, Britain, Australia, South Korea and the US.
But many local election officials in isolated towns said on Sunday that they were still waiting for election materials, including indelible ink to mark voters and prevent multiple attempts to cast ballots.
The Philippines has 45 million registered voters, including a half-million of the 7.5 million Filipinos who live abroad.