Suggestions that a youth jail might be built on a greenfield site in one of the fastest growing suburbs in Victoria has drawn the ire of locals.

The state government is planning a new youth detention centre with Fairfax Media reporting on Tuesday that the 250-bed centre would be built in Werribee South.

Transport Minister Jacinta Allan wouldn't confirm a location for the new centre on Wednesday, saying only that "details are being worked through".

But Werribee residents were up in arms about the suggestion that it could be in Melbourne's outer west.