The US Homeland Security Department says the government has reunited 522 children separated from adults as part of a “Zero Tolerance” initiative.

Reacting to public disgust and criticism, plans are being implemented to return more children in the days ahead.

The department said in a statement US Customs and Border Protection expects a small number of children separated for reasons other than zero tolerance would remain separated.

Those cases would likely involve children where it is not possible to confirm a familial relationship with those claiming to be their guardians.

President Donald Trump on Wednesday signed an executive order to end his policy of separating immigrant children from their families on the US-Mexico border, after images of youngsters in cages sparked outrage at home and abroad.

This protester outside a border facility wipes away a tear as she calls for a revolt against the Trump administration. Photo: AAP

The department also said the Department of Health and Human Services (HHS) has 2053 separated minors in HHS-funded facilities.

Government agencies are working  “to foster communications and work towards reuniting every minor and every parent or guardian via well-established reunification processes.”

Currently, 17 per cent of minors in HHS funded facilities were placed there as a result of the Zero Tolerance enforcement effort.

The remaining 83 per cent arrived in the United States without a parent or guardian, it said.

-with AAP