Northeasterly winds were expected to drop from 20-25km/h to less than 10km/h this evening, aiding the firefighters' efforts.
St John had received no reports of fire-related injuries from the island.
Extra police officers will be on the island overnight.
The cause is being investigated and initial reports of the fire being suspicious could not be confirmed, said a Northern Fire Communications spokesman. It is unknown if the emergency was caused by a 5000 square metre vegetation fire tackled on Sunday reigniting.
Meanwhile a suspicious scrub fire that burned 200ha of scrub near the Kaipara Harbour is also under control.
The fire started on DoC land at Kellys Bay on the Pouto Peninsula, southeast of Dargaville, yesterday morning.
Four helicopters and 80 ground crew battled to bring the fire under control.