UPDATED 8.16pm: Five homes have been evacuated, roads closed and planes warned from flying above Marlborough as a huge scrub fire continues to burn.

Eight helicopters and eight fire crews are fighting the blaze, which spans across three kilometres of felled forestry and is spreading onto standing trees.

Principal rural fire officer Richard McNamara said the fire's jumping and creating spot fires ahead of itself, which is making it difficult to control.

He said the fire's burning under extreme conditions, and if they get a change in the wind, or another slope catches, the whole picture could change considerably.