A couple who found a woman washed up on a West Coast beach say it's a miracle she and her son survived.
The woman was swept into the Arahura River, north of Hokitika and then out to sea after a car crash early on Saturday morning.
Her six-year-old son had tried to get his mother out of the vehicle before walking almost two kilometres in the dark to find help.
The 41-year-old woman was found the next morning walking out of the sea by Bronwyn Vercoe and her partner, John.
Vercoe told Morning Report they were having breakfast when they saw a woman trying to climb the fence.
"She climbed the fence, walked through the paddocks towards the house. I ran down with a towel because she was soaking wet. She looked at me with fear in her eyes."
"I told her 'It's okay, it's okay, what happened' and she said 'I've just been washed up'. Absolutely unbelievable."
Vercoe said her house was about seven kilometres north of where the woman went into the river.
The woman told Vercoe she had come up the coastline and saw the helicopters that were looking for her were 'looking in the wrong place'.
"She told me she was fearful for her child. We didn't know anything was amiss. That's when we thought we better ring 111 and get this lady some assistance."
Vercoe said the police then informed them that the woman's son was safe.
"She felt incredibly cold, she was shaken, she was scared and she was scared for her son. My heart absolutely went out to her.
"We took her inside, put a dressing gown on her and started plying her with Milo. That's when the police and emergency services arrived," Vercoe said.
"It was a miracle, an absolute miracle."
Vercoe said she wouldn't swim in the West Coast beaches, and the woman who got caught in the tide was lucky.
"She said she got caught in the undertow. I believe that she was local.
"I believe she must've been a strong swimmer, and there was someone looking out for her ... it wasn't her time. She was incredibly, incredibly lucky."
The woman has been treated for hypothermia at Greymouth Hospital.