Newborn lambs are in the firing zone of an icy blast for the next 48 hours in the deep south

Snow settled on the ground in Invercargill this morning and flights are grounded at Queenstown - and motorists warned off southern highways.

WeatherWatch head analyst Philip Duncan says says lambs are vulnerable to wind chill and temperatures falling to minus 10 degrees in the hills.

He says they're unlikely to survive overnight unless farmers are out there to help them.

Duncan says the timing is really bad for lambing.