Warkworth resident Becky Watson said she heard helicopters in the area at 4am.
"[They were] flying so low it woke me up."
Further information will be provided by Superintendent Tusha Penny, Waitemata District Commander, at a media conference later today.
State Highway 1 is closed between Woodcocks Rd and Silverdale.
Diversions are in place for southbound traffic at Woodcocks Rd, where traffic is being diverted on to SH16.
For Northbound traffic, there is a diversion in place at Silverdale, where traffic is being diverted to Kahikatea Flat Rd, through to SH16.
Earlier, a police spokeswoman said the road was closed because of a "police operation underway on SH1".
"We don't have any further details we can provide at this stage, but we will provide more information as soon as we can."