District Health Boards are being told to pay up or they could risk losing more of their sonographers, who work with ultra-sound imaging.

The association representing sonographers says the situation has escalated to a crisis point with more sonographers working in the private sector than the public.

Spokeswoman Dr Deborah Powell says with private rates of pay 25 percent more than that of public it's obvious why the DHBs are losing out.

"Well DHBs do have financial restrictions we do appreciate that. I don't think the District Health Boards can blame their financial paralysis. A. Because we've got very few people involved in this, and secondly the DHBs are actually paying more anyway."

Ms Powell says the DHBs are having to pay out more for casuals as a result of the shortage.