Asylum seekers have been told they will lose their welfare payments, bridging visas and right to seek asylum unless they urgently submit applications for protection, as the Turnbull government cracks down on the "legacy caseload" of boat arrivals.

The Department of Immigration has begun issuing warning notices to hundreds of the approximately 12,000 asylum seekers in the community who came to Australia by boat prior to July 2013 but are yet to make applications for refugee status.

They are being given 60 days to apply, including all necessary documentation, with some who have already missed the deadline being told their support payments have been suspended and they now face losing their ability to claim asylum.

Immigration lawyers and refugee advocates are in despair over the crackdown, arguing it has created a rush on legal services and is leaving some asylum seekers unable to submit their application or forcing them to apply without legal help.