Filipino activists accused President Ferdinand Marcos Jr's government Thursday of carrying out a "witch-hunt" against rights defenders as they held rallies for the 51st anniversary of the imposition of martial law.

Hundreds of people marched in Manila calling for the release of victims of forced disappearances and the abolishment of an anti-communist task force, set up by former president Rodrigo Duterte, that has been accused of targeting government critics.

Rights group Karapatan said the Marcos Jr administration was using the task force to "witch-hunt activists, human rights defenders and other dissenters", while enabling the military and police to "perpetuate repression reminiscent of the martial law era".

Marcos Jr's dictator father, Ferdinand Marcos, imposed martial law in 1972, unleashing his security forces on rivals, critics and dissidents.

Amnesty International estimates thousands of people were killed and tens of thousands tortured and imprisoned in the brutal crackdown.

Activists said rampant human rights abuses have continued under Marcos Jr, who has kept up Duterte's deadly war on drugs, as well as his National Task Force to End Local Communist Armed Conflict.

Rights groups say eight activists have been "disappeared" since Marcos Jr became president in June 2022.

There have been more than 400 drug-related killings during the same period, according to a monitoring group.

"It's like we're still living in the shadows of 1972. This regime doesn't care about human rights," Renato Reyes, secretary general of the leftist alliance Bayan, told protesters.