Three helicopters are battling a large scrub fire threatening a forestry block near Dipton in Southland this afternoon.

Fire and Emergency New Zealand communications shift supervisor Andrew Norris said three fire crews and three aircraft were fighting the blaze, about 30-40 hectares in size, and consuming scrub and windrows.

The blaze was threatening a commercial forestry block just west of Dipton, near Dipton Flat Rd, Mr Norris said.

Crews were called just before 2pm.