Two helicopters are fighting a large scrub fire that has blocked the main road between Nelson and Christchurch this afternoon.

Waka Kotahi NZTA said State Highway 59 had been blocked between Murchison and Springs Junction. It told motorists to either delay their journeys or avoid the area.

"Northbound traffic can detour on State Highway 7, onto State Highway 69, onto State Highway 6. Reverse for southbound."

Fire and Emergency told 1News that two appliances were called to the scene at about 11am to a report of a vegetation fire.

When crews arrived, they discovered a large scrub fire and requested a helicopter - with another requested due to winds pushing the fire across the terrain, according to FENZ.