A spreading scrubfire has closed State Highway 1 at Dome Valley, about five kilometres north-west of Warkworth.
Firefighters are battling the blaze with four trucks, two tankers and two helicopters.
The fire was first reported to fire communications at 1.30pm, with a size of about 5000 square metres.
Fanned by steady winds, it spread to cover about 64,000 square kilometres in an hour, Fire Service senior communicator Tania Matthews says.
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"Hopefully we can contain this fire quickly, before it causes too much disruption to traffic - it's a very busy road," she says.
Police have diverted traffic at Kaipara Flats Road for northbound vehicles and onto SH16 at Wellsford for those southbound.
