Thirty "drug dealers" were killed in the first four days after Rodrigo Duterte was sworn in as Philippine president on June 30, police said, announcing the seizure of nearly $20 million worth of narcotics but sparking anger from a lawyers' group.

Duterte won the election in May on a platform of crushing crime, but his incendiary rhetoric and advocacy of extrajudicial killings have alarmed many who hear echoes of the country's authoritarian past.

Oscar Albayalde, police chief for the Manila region, said five drug dealers were killed on Sunday in a gun battle with police in a shanty town near a mosque near the presidential palace.