State Highway one at Dome Valley, near Warkworth in Northland, has reopened after a major scrub fire closed it for about five hours today.

The highway was closed for safety reasons after a blaze spread rapidly in the windy conditions, covering about 240,000 square metres, before firefighters contained it.

Smoke from the smouldering scrub was earlier causing poor visibility on the highly-trafficked, high accident area.

The fire was first reported to fire communications at 1.30pm, with a size of about 5000 square metres. Fanned by steady winds, the fire had spread to cover about 40,000sq m in an hour, Fire Service senior communicator Tania Matthews said earlier.

Fire crews were continuing to dampen down hotspots in the area.