A mother and toddler waited two hours in the dark amid heavy rain with two flat tyres after hitting a pothole on a stretch of highway that sparked traffic chaos two days earlier.

Fortunately, Eduarda Massa was driving over the Kaimai Ranges at 5am and stopped to help out the stranded duo.

Massa herself hit a pothole on the way, but it did not damage her car.

She says the potholes were 'pretty big” and it was pouring down before dawn.

A social media post warned drivers to be cautious with 'at least 20 cars with blown tyres and rims” on the Kaimai Ranges, which connects Waikato to Tauranga.Video: Supplied/Stuff.

'I couldn't see any signs or cones, not sure if it was because it was dark and raining.”

Massa saw two more cars with damaged tyres on the side of the road while she was helping the woman on Sunday.

'We called a tow truck to come and pick up the car and I drove the mum and the kid to their relative's place.

'She told me both front tyres were popped, so she couldn't even drive further with it.”

It follows an incident on Friday, where 'at least 20 cars with blown tyres and rims” were parked up on State Highway 29, which connects Waikato to Tauranga.

Video posted to social media by a motorist shows a line of cars pulled over in the wet conditions.

One of the comments says the number of cars pulled over with blown tyres reached 31 at one point.

Jennifer Niederer, another victim of the pothole carnage, says it totally wrecked her car wheel.

Niederer says she couldn't see the pothole because it was raining heavily, and the hole was filled with water.

'Obviously neither did the other 17 cars that hit the pothole.

'It was very frightening, and we were lucky to be assisted a very nice young man who helped us get the tyre off in the mud on the side of the road.”

Waka Kotahi NZ Transport Agency confirmed that new potholes had formed on both directions over the weekend following Friday's incident.

Bay of Plenty system manager for Waka Kotahi Roger Brady says a crawler lane is closed (before Hanga Rd, near the summit) and traffic management is in place, along with a speed restriction.

In regards to Friday's incident, he says the road was inspected earlier in the day and there were no issues reported. Contractors were on site within the hour after being notified of road damage about 5.30pm, he says.

They found a series of potholes over an approximately 9m section of the highway, as opposed to one big pothole.

Persistent rain and heavy traffic had caused the surface to deteriorate rapidly.

A lane of traffic was shifted to enable them to safely fill the holes, Brady says.

Repairs would also be undertaken to strengthen the road structure on specific areas of SH29 next month.

'This winter has seen a significant increase in potholes across the country, compared to the past three years. This is down to a combination of current network conditions and the wet winter.

'Water is the primary cause of potholes. If there is a crack in the road surface, or a displaced stone, it will allow water to sit in the road surface.

'As vehicles drive over the ponding water, tyres create hydraulic pressure, forcing the water down into the pavement. Areas with cold overnight temperatures will cause the water to expand and contract, which creates pressure on the road surface and underlying pavement.

'Over time, as vehicles continue to run over the pothole, it will grow in size as weakened areas break off. Sections of road that are due for renewal are often the worst affected areas as the pavement and surface are weaker and are starting to fail.”

- Avina Vidyadharan/Stuff.co.nz.