A fatal crash that closed a vital link between the Waikato and Tauranga may have been caused by a boulder in the middle of State Highway 2.

The highway through the Karangahake Gorge, between Paeroa and Waihi, remains closed this afternoon as police investigate the cause of the incident, which is being described as a 'tragic quirk of nature”.

Police are investigating a two-car crash in Karangahake Gorge which has killed one person. Photos: Supplied.

Inspector Freda Grace says emergency services were still at the scene of this morning's crash near the intersection of SH2 and Rahu Road in the Karangahake Gorge.

'The crash, which happened about 10.40am, is currently under investigation by the Waikato Serious Crash Unit,” says Freda.

'It's too early to confirm what caused the collision between an eastbound Holden Commodore Sedan and a westbound Peugeot car.

'What I can say, however, is that we are looking into what part, if any, a large rock (similar in size to a medicine ball) found in the eastbound outside passing lane may have played in the crash.

'It appears the man driving the Commodore may not have seen the boulder and struck it, causing his car to career into the path of the Peugeot.”

Freda says the sole occupant of the Commodore died in the crash, while the female front seat passenger in the Peugeot suffered serious injuries and was airlifted to Waikato Hospital.

The male driver of the Peugeot suffered minor injuries and initial indications are that alcohol was not a factor in the crash.

'There is still a lot of work to go through before we can conclude what has occurred,” admits Freda.

'State Highway 2 is expected to be closed for some time and this has placed a strain on other roads.

'It is a key route through our district linking the Ports of Tauranga and Auckland and is used by high numbers of heavy vehicles.

'Traffic has been diverted north and south via SH2-SH27-SH24 and SH29 over the Kaimai Range for southbound traffic and the reverse route for northbound travellers.

'Drivers are advised to expect delays and exercise caution and patience while using this alternative route.”

Freda says today's incident highlights the need for motorists to maintain their situational awareness at all times.

'Road safety is no accident,” she adds.

'By having drivers and vehicles fit for the road we can hopefully work to prevent tragedies such as this morning's from occurring.”

Update Karangahake Gorge fatal closes SH2 - Waikato Police investigating this morning's fatal collision that close... http://t.co/uAoCCUDOYA

— New Zealand Police (@nzpolice) July 30, 2015