Six fire crews are battling a "well involved" Nelson house fire and searching the property to see if anyone is inside.

Southern fire communications shift manager Tim Reynolds said two appliances from Stokes fire brigade were sent after several people made 111 calls just before 9pm.

When the crews arrived at the house on Cawthron Cres they found a large blaze and two brigades each from Richmond and Nelson were then sent to the scene, Reynolds said.