Five of the victims areadults and one is a newborn baby.
Four adults in a vehicle travelling north were pronounced dead at the scene. The driver of the second southbound car and a newborn baby also died at the scene.
Police said the front-seat passenger of the southbound car - a woman - was airlifted to Wellington Hospital with critical injuries. An 8-year-old girl has been taken to Waikato Hospital for treatment.
Police said the Serious Crash Unit was still investigating the circumstances of the crash, but said it was clear that the vehicles have impacted head-on.
"At the time of the crash, the weather was clear and the road was dry. The crash occurred on a slight right-hand bend of the road."
"The tragedy will affect a large number of people in our community. Our sympathies and condolences go out to the family, friends and loved ones of those involved.''
Officers said the priority now was making sure support was provided to those who need it following the "heartbreaking'' crash.
Whanganui Sergeant Colin Wright said four people were in each car that collided head-on on State Highway 3. Four of the dead were elderly. They were travelling west, towards Hawera, when the two cars collided on a sweeping bend near Waverley Racecourse shortly after 11am. Two people from the other car are also dead.
"They're still being treated [and are] going to be going to various hospitals," Wright said.
"At the moment we're just investigating exactly what's happened."
It was earlier reported, two rescue helicopters landed at the crash and a third was on its way. Two fire engines, three ambulances and multiple police officers were at the crash.
Six people are dead and three have critical injuries after a horror crash near Waverley in South Taranaki. Photo / Stuart Munro
Wright said the road will be closed for a number of hours.
Cars are being diverted off SH3 down Ihupuku Rd and motorists are advised to avoid the area.
A local woman leaving work 500m from the crash described the scene as "a mess".
— Waka Kotahi NZTA Central North Island (@WakaKotahiCNI) June 26, 2018
Waverley is in the South Taranaki district, 44km northwest of Whanganui.
Taranaki police this morning warned drivers about ice on the road, after four crashes since 5am.
"We need motorists across Taranaki to be extremely cautious on the roads this morning after four crashes caused by ice on the road since 5am," police said.
"Any patches of road which appear wet will likely be ice and should be treated as such.
"Police are also advising people to check their vehicles and tyres are roadworthy and ensure all windows are completely clear of ice before getting behind the wheel."
