A young female tourist from Germany has become the latest casualty in a holiday road toll which stood at 18 last night.

State Highway One north of Hunterville was closed after the woman, a passenger in a van travelling north towards Taihape, was killed in a head on-crash with a ute, which police said crossed the centre line.

The crash, about 12.45pm, pushed the road toll for the holiday period, which ended at 6am today, to 18 people killed since Christmas Eve.

It compares with 12 road deaths during last summer's Christmas-New Year break and 13 the year before.

Inspector Bruce MacKay said last night the latest victim was a young German tourist, although she had yet to be formally identified.

She died at the scene and her male driver was flown by rescue helicopter to Palmerston North Hospital with serious injuries, including multiple fractures.

The driver of the ute, also male, was taken to Wanganui Hospital but Mr MacKay said his injuries were less severe than those of the van driver.

Palmerston North rescue helicopter pilot Marc Bridgeman said the crash happened on a straight stretch of road.

"As you'd imagine from a head-on, high-speed collision, there's pretty significant damage out there."

Other traffic had to be diverted to unsealed roads, which were not suitable for heavy vehicles or camper vans, whose drivers were advised by police to take alternative highways through the central North Island.

The grim holiday toll stood in contrast with reasonably free-flowing traffic back to Auckland from Northland, amid which the Herald noticed exemplary driving by motorists, including no speeding or dangerous overtaking.

By 4pm, the only bottleneck was around the Warkworth intersection of SH1 with roads to the eastern beaches.

Traffic also flowed well over the new two-lane Kopu Bridge from the Coromandel Peninsula, although the AA reported congestion late in the afternoon past Mangatawhiri on SH2.

The Transport Agency's Waikato highway manager, Kaye Clark, said about 6pm that the organisation was keeping an eye on traffic building up at the intersections of the Kopu-Hikuai road with the Thames-Paeroa route and of SH25 with SH2 west of Kopu.