Police are appealing for help in tracking down the men who robbed a regional council employee at knifepoint, then threw bleach into his eyes and face.
It is not known whether the victim, who was discharged from hospital on Monday night, will suffer permanent sight damage.
The shocking attack occurred about 7am on Monday on State Highway 10, at the Oromahoe Rd turnoff about 10km south of the Kerikeri crossroads.
Detective Sergeant Sam Bindon, of Kerikeri police, said the victim had been driving from Kerikeri to Whangarei when a vehicle came up behind him flashing its lights.
The Kerikeri resident pulled over in a gravel layby next to Oromahoe Rd, where he was assaulted by at least two men. He was threatened and a knife was held to the side of his face, leaving him with cuts.
His assailants took his cellphone and wallet, which they appeared to have searched before throwing it away at the scene.
They then threw bleach into his eyes and face before driving off, continuing south towards Pakaraka.
Mr Bindon said a local man saw the victim in distress and stopped to help, calling an ambulance and police.
The call came in at 7.30am but it was not known exactly how long the victim had been trying to get help. He was treated at the scene then taken initially to Bay of Islands Hospital in Kawakawa.
Mr Bindon said it was too early to say if the victim would suffer lasting effects to his sight. With the man still being treated in hospital yesterday police had not yet been able to take a statement from him, so the attackers' motive was as yet unclear.
Mr Bindon said police wanted to hear from anyone travelling on SH10 between Kerikeri and Oromahoe around 7am yesterday who saw the man's ute being followed by a car flashing its lights.
The victim had been waiting for a safe place to pull over so could have been followed for some time.
The only description of the offenders' car so far was that it was white with a sloping bonnet, possibly a Honda Accord or similar. The victim was driving a white Nissan Navara twin-cab ute with Northland Regional Council signwriting.
Monday morning was foggy and the cars stopped well off the road, so the attack itself might not have been seen. However, with plenty of traffic on the roads at that hour someone must have seen the ute being followed by a car flashing its lights.
Mr Bindon appealed to anyone who may have seen the attackers or could describe their car to call the Kerikeri police station on (09) 407 9211. Information could also be passed anonymously to Crimestoppers on 0800 555 111.
A regional council spokesman said management had been in contact with the staff member's family and were providing support as needed.
Senior Sergeant Peter Robinson advised anyone being followed by another vehicle flashing its lights to wait for a safe place with plenty of visibility and other people around before pulling over.