Jacinda Ardern says a Government department made a "huge oversight" when they placed a sex offender in the same motel as at-risk children.

A recent article by Stuff says that police are investigating after convicted sex offender Roland Jeffries was placed in a motel, believed to be in the lower North Island, by the Department of Corrections.

There are concerns that he abused vulnerable children who were also housed in the motel.

Jeffries, who was subject to a 10-year extended supervision order after a lifetime of sexual offending, has since been placed back in prison, Stuff reports.

Speaking at a post-Cabinet address today, Ms Ardern expressed her concerns over the matter.

"It seems to be a case where Government departments have not communicated with one another it seems to be a huge oversight and we have to expect better.

"When Government departments put two categories of at risk people into the same environment then we have to be accountable for that, I don’t think anyone would think that would pass the test of a sensible placement," the Prime Minister said.