Labor's deputy leader Tanya Plibersek has called for children to be released from Nauru and mainland detention centres as soon as possible, describing Australia's asylum seeker politics since 2001 as "nothing less than toxic".

Her strong stance places her at odds with shadow immigration spokesman Richard Marles, who on Wednesday defended offshore processing, including for children.

Responding to a letter from 900 prominent academics calling for children to be released from detention, Ms Plibersek said Australia had a moral obligation to do more to address the global refugee crisis and said the debate domestically had "lost rationality, compassion and respect".