Philippine Catholic leaders say they are powerless to stop a growing number of extrajudicial killings that have come with President Rodrigo Duterte's war on drugs.

"What I predicted is happening, and the Church is powerless to stop the killings," Fr Amado Picardal, head of the Philippine bishops' Commission for Basic Ecclesial Communities, told ucanews.com.

He said the killings were "already unstoppable", adding that some Church leaders are losing hope.

Fr Picardal, who has linked the president to a death squad allegedly responsible for the killings of more than 1,400 people, warned of "dark prospects" for the Philippines following Duterte's election in May.