The first occurred 3km south Luggate, east of Wanaka, about 6pm when a grey Ford Falcon left the road and rolled, police said.
The only passenger in the vehicle, 54-year-old Wanaka woman Rosemary Margaret Lamb, died. The vehicle's 62-year-old driver remains in a serious condition in Dunedin Public Hospital.
The crash came only hours after a woman was seriously injured in a three-car collision near Milford Sound.
Yesterday's second fatal crash, in the Tararua District, was reported to emergency services about 7.30pm.
Police said it appeared a vehicle left Mangamaire Rd and collided with a power pole.
The sole occupant, 25-year-old Palmerston North woman Monique Miers, was pronounced dead at the scene.
It was unclear what factors had led to the crash, police said.
A short time later, a child was killed when a car hit a power pole south of Tauranga at 7.45pm.
St John Western Bay of Plenty territory manager Ross Clarke said the young child was a preschooler.
The child had been travelling with a woman along Oropi Rd when their car crashed into a concrete power pole near Castles Rd.
The dark blue sedan ended up in a nearby paddock.
Oropi Rd resident Krystal Walsh told the Bay of Plenty Times she saw up to eight emergency service staff were treating two patients on the ground in the paddock.
"They tried adrenaline, they had a defibrillator but it didn't seem to make any difference," she said.
"From what we could see, three were with the baby and four with the woman. Then they stopped working on the baby and started resuscitating her," she said.
Ms Walsh said the stretch of road was dangerous and had been especially slippery last night.
Northern Fire Communications shift manager Megan Ruru said it appeared a small child was trapped in the car immediately after the crash.
The child was removed to an ambulance for medical treatment but later died, Ms Ruru said.
The road was closed for several hours as contractors worked on downed power lines.
The driver was a local woman who did not sustain any injuries but was taken through to Tauranga hospital, police said.
The death came two days after a man was killed while walking along SH2 at Te Puna.
Grant Coley, 59, died when he stepped out in front of traffic travelling north. He was struck by a truck.