Perth man allegedly abused 24 children

West Australian police allege about 3.8 million child exploitation videos and images were found on the devices, some of which allegedly showed him offending against the children.

He is alleged to have sexually abused 24 boys and girls, aged from three to 13, between 2015 and last year.

Detective Inspector Hamish McKenzie said it would be alleged the man, who cannot be named for legal reasons, knew the victims through family and friends.

"(It) is one of the most significant child abuse investigations ever conducted in Western Australia insofar as how many images were located and how many victims we will allege have been abused," Det Insp McKenzie told reporters on Wednesday.

The man is facing more than 400 charges including sexually penetrating a child aged under 13 and producing child exploitation material.

He is next due to face court on April 22.