The Morrison government’s allowing people on student visas to work unlimited hours created a “Ponzi scheme” that was exploited ruthlessly by some education agents, an international education conference was told on Wednesday.

The move also heaped pressure on the Department of Home Affairs, which is trying to process a backlog of one million visas, with the more complicated ones linked to questionable applications being shunted to the back of the queue, said Labor backbencher Julian Hill.