Philippine troops killed six Communist rebels Sunday in a clash north of Manila.
An infantry unit on routine patrol ran into a 40-man unit from the New People's Army, touching off the fighting.
A military spokesman Lieutenant Colonel Buenaventura Pascual, says troops are still in action, rooting out pockets of resistance.
The government has not reported any casualties.
The NPA is the armed wing of the Communist Party of the Philippines. Both groups are listed as terrorist organizations by the United States and the European Union.
Some information for this report provided by AFP and AP.