Police said diversions are in place at the SH2 intersections of State Highway 50, Charlotte Rd and Kopua Rd.
"A diversion is in place, however we are asking motorists to avoid the area and delay travel for the next couple of hours," the police spokeswoman said.
All three motorists killed were traveling in the car, while the truck driver was airlifted to Hawke's Bay Hospital. Police said the truck driver was admitted to hospital and was being offered victim support.
The road will remain closed for the next few hours.
According to a Waka Kotahi NZ Transport Agency - Hawke's Bay and Gisborne spokesman, the SH2 southbound lane is closed with detours in place near Charlotte Rd.
"Northbound remains open," the spokesman said. "Please take extra care while passing and expect delays in the area.
"Contractors are en route," the spokeswoman added.
The accident followed two serious SH2 crashes in the region on Monday, before midday.
A 6.16am crash involving a light truck was the first of two accidents that closed parts of SH2.
A man in his 30s and a male teenager were taken to hospital from the crash scene near Te Kahu Rd. The pair had serious to moderate injuries but were later reported to be in a stable condition.
The highway was closed for just over an hour, before one lane was opened between 7.35am and 11am.
Police were also called to a two-vehicle crash near the Omahu Rd and SH2 roundabout at 10.15am.
One person had to be freed from one of the vehicles by Fire and Emergency crew.
A man in his 20s was taken to Hawke's Bay Hospital, where he was in a stable condition.
Both of the earlier accidents were in fine weather conditions, with dry roads and good visibility.
