Manila: Four people were killed and two dozen wounded when two rival politicians exchanged gunfire in northern Philippines, police said on Friday.

Regional Police Chief Ismael Rafanan said fighting erupted late on Thursday in Jaen town in Nueva Ecija when the convoy of a mayoral candidate was fired upon by suspected supporters of a congressman allied with President Gloria Macapagal Arroyo.

"We're conducting a thorough investigation because we've been hearing so many versions of what had really happened," Rafanan said.

On May 14, Filipinos will vote candidates for half of the 24-seat Senate, all of the 235-member House of Representatives and nearly 18,000 of local government seats.

In the run-up to and during elections, private individuals are barred from carrying firearms but the ban is widely flouted with an estimated 300,000 unregistered guns in circulation.