A "horrible" and "sad" scene where a baby sat crying in a car seat while his parents lay dead nearby is one of many that plagued the first wet weekend in months in Waikato and Northland.

Eight people were killed in five separate road smashes on Saturday and Sunday.

Claire Allen and James New were among the first to the scene of the second fatal on Saturday about 5.40pm. "Panic mode" set in when they saw an infant, still strapped in its car seat, being pulled from the car.

Allen collected blankets and ran barefoot across shattered glass to comfort it.

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TOM LEE/STUFF The crash in Cambridge was one of four fatals that left five people dead in Waikato over the weekend.

"It was really horrible and a really sad thing to see," Allen told Stuff on Sunday. "James has two young girls, and all I could see was them."

The baby, a boy, looked "not a year old".

She said it became clear when fire crews arrived that his parents were dead in the ute.

"He was crying, it was very weak, but hearing the cry was so comforting.

"It was scary and there was blood everywhere but he did seem okay. He started off well but then I think he started going into quite a bit of shock."

Allen and New said the stretch of road was "dangerous" and that it had been raining "torrentially" moments before the crash.

"I've always been huge on car seat safety, but [the seat] really did save the baby's life. It was in perfect condition," Allen said.

"It's crazy because we're never going to know what happened to that baby, but it's so heartbreaking that he's lost two adults that were really close to him."

A Waikato Hospital spokeswoman said the baby remained in a critical condition in the Intensive Care Unit on Sunday afternoon.

TOM LEE/STUFF Cambridge Volunteer Fire Brigade chief Don Gerrand said the phenomenon known as "summer ice" was one to be wary of.

Waikato Serious Crash Unit Sergeant Steve Jones said the occupants of the Toyota Hilux were visiting family in Cambridge, and were heading south at the time of the collision.

Early indications suggest the Hilux lost control entering the bend and went into a clockwise rotation with an Isuzu light truck consequently T-boning the passenger side of the vehicle, he said.

Many of the incidents over the weekend seemed, Jones said, to be caused predominantly by a spell of rain after the long dry period.

Cambridge Volunteer Fire Brigade chief Don Gerrand said the phenomenon known as "summer ice" was one to be wary of.

TOM LEE/STUFF The crash between a ute and truck occurred on Cambridge Rd, following a 65kmh signposted corner.

"After such long periods of dry, as soon as you introduce some rain, the roads do become skating rinks.

"All of the grease and products in the tarseal are brought to the surface, and mixed with water, it then becomes slippery."

According to the Transport Agency, the greatest risk for crashes is shortly after the rain starts.

Gerrand attended the crash and said, on arrival, crews checked the two occupants of the ute for any signs of life. At that stage, the child had been removed from the car.

The double fatal was one of four crashes that left five people dead and others injured in Waikato over the weekend.

TOM LEE/STUFF Two adults lost their lives and a baby was left in critical condition after a crash near power pole in the foreground.

One person died and several were injured after two cars collided on Morrinsville-Tahuna Rd, north of Morrinsville, about 10.30am on Saturday.

About 7.15pm, police were again deployed, this time to State Highway 25 near Pipiroa. They later confirmed the sole occupant in the single-vehicle died after the car hit a power pole.

And on Sunday, one person was killed in one of two separate crashes near Piopio about midday. The main road between Hamilton and New Plymouth was closed for several hours as Serious Crash Unit staff analysed what went wrong.

In Northland, three people were killed and a child was left in a critical condition after a single vehicle slammed into a tree about 2.13am on Sunday.

With Metservice predicting another dry week for Waikato, Gerrand encouraged people to change their driving habits according to the weather.

"Our driving attitudes have got to change. Speeds have got to drop, vehicles have to be up to standard, and stopping distances have got to be longer," he said.