The car was believed to have spun out of control before smashing into the truck. Police said the car crossed the centre line but the cause was yet to be established. The female driver of the car and two rear-seat passengers, one male and one female, died at the scene. Police confirmed both in the rear were not wearing seatbelts.
The truck driver was shaken but not injured.
Police confirmed the car's passengers were foreign nationals but said no further details, including their nationality, would be released until next of kin had been notified.
SH1 was closed into the evening as emergency services worked to free the trapped bodies from the wreckage. Diversions were put in place at Wiltsdown Rd and Rollett Rd.
Less than two hours after the triple fatality, another person died in a crash on the SH1 Northern Motorway in Auckland, between Greville Rd and Oteha Valley Rd.
"A four-wheel-drive vehicle has left the motorway, crashed down a bank into a couple of lamp posts," a police spokesman said.
"The driver, despite CPR attempts, is deceased at the scene."
Earlier yesterday, two women died in a head-on collision near Thames, on SH25 at the intersection with Pipiroa Rd, between Waitakaruru and Kopu. A Thames-bound Mazda Demio and a Volkswagen Passat travelling north collided about 7.45am, with the two women in the Mazda dying from their injuries.
It was initially believed both women were Australian. However police later said it had been established one of the women was a New Zealander and the other Australian.
Work to formally identify the women and notify their families was under way, police said.
The sole woman occupant of the Passat was freed by firefighters and airlifted to hospital by helicopter in a serious to critical condition, Sergeant Dave Reid of the Waikato district command centre said.
The busy rural highway, which links Coromandel to Auckland, was closed until mid-afternoon while a lengthy extraction process was completed.
Three fatal accidents
• 7.45am Head-on collision near Thames, two dead
• 3.50pm Car and logging truck collide north of Tokoroa, three dead
• 5.38pm Crash on Northern motorway, one dead