Four rescue helicopters have rushed to the scene of a two-car crash on the Desert Road that blocked State Highway 1.

Eight people needed medical help after the cars collided around 3pm, 5km north of the Tree Trunk Gorge Rd intersection.

The Desert Road has since reopened, but due to damage on the road there will be ongoing delays while repairs are made, police said.

Emergency services were soon at the scene, including four rescue helicopters, three ambulances, and a first response unit.

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On arrival, they found six people were in a serious condition.

Five of them were flown to Waikato Hospital, and the sixth was flown to Rotorua Hospital.

The two other peoples involved had moderate injuries. They were taken to Taupo Hospital by road ambulance.

No information was given about the age or gender of the patients.

Police are advising motorists to take alternate routes.

The road is blocked in both directions and traffic is being diverted.

A diversion is in place north of the crash, at the intersection of SH1 and SH46, Rangipo.

South of the crash, a diversion is in place at the intersection of SH1 and SH49 at Waiouru.

Eye witnesses have taken to social media to praise the quick response from other motorists.

Kiriana Eparaima-Hautapu said it was "amazing" to see off-duty doctors and nurses leap into action, taking charge of the scene while waiting for the ambulances to arrive.

Kylie Brooks tweeted that Desert Road southbound was "incredibly backed up".

She saw three fire engines racing past as she sat in her car.

Brooks was then directed to the diversion by emergency personnel, who warned there would be a two- or three-hour delay for her journey.

The official New Zealand Transport Agency estimate is that the diversions will add 40 minutes extra to travel times.