"Evacuate immediately! Evacuate immediately! A tsunami is coming!"

The little white car with the loudspeaker tore past the Okawa Primary School.

Despite the warnings being screamed at them, the teachers seemed paralysed, unsure what they should do.

Koharu Hiratsuka, 12, was killed in Japan's 2011 tsunami. ( Supplied: Naomi Hiratsuka )

Koharu Hiratsuka looked at her friends. They were terrified.

How could a tsunami reach the school? The sea was four kilometres away.

Twelve-year-old Koharu had sheltered under her desk when the earthquake had struck minutes before. Then her class had followed their teacher out onto the school oval, just as they had been taught in the evacuation drills.

From the open ground of the oval, the teachers and students couldn't see the Kitakami River next to the school.

If they could, they would have seen the water level dropping. Like a snake, the tsunami was drawing back, preparing to strike.

Some of the teachers began arguing. One suggested they all evacuate to the hill on the edge of the oval. Another said they were better off staying put.

Then, more than 45 minutes after the earthquake, finally a decision was made.

They would move to a high spot near the green bridge that crossed the river.

The teachers bellowed out instructions, and everyone began to move.

But it was too late.

Suddenly, water started to spill over the embankment of the river towards the school.

"The children tried to run away," one survivor recalled.

"Some of the children and the adults were washed away. The village around the school vanished in about three seconds."

The tsunami had also engulfed Koharu Hiratsuka.

The town of Rikuzentakata (pictured) is about 60km north of the Okawa Primary School. ( ABC News: Mark Willacy )

From that moment, she disappeared, taken by the unstoppable wave. Seventy-three other children and 10 teachers also died.

Naomi Hiratsuka's daughter's remains were found five months after she disappeared. ( ABC News: Mark Willacy )

For months, Koharu's mother Naomi would spend almost every waking moment searching for her missing daughter.

I would go to see Naomi as she dug through the fetid swamp left by the tsunami.

I would watch as body after body was uncovered from this wasteland around the Okawa Primary School.

Months later Naomi recalled the experience.

"There were several excavators being used by the firefighters," she said.

"Whenever they shouted 'We found one', I would race over and see if it was my daughter or another child I knew."

But each time Naomi would walk away, no closer to finding Koharu.

Sorry, this video has expired The beauty of Fukushima's cherry blossoms jars against the piles of bags filled with earth and debris.

Eventually, the official search around the school was called off.

But Naomi refused to stop.

She got her excavator's licence so she could continue to look for Koharu and other missing kids.

"I understand that they're dead, but I can't leave the dead body underneath the rubble, in the mud, in the river or in the water," she told me one day as she stood next to her excavator.

"I want to get them out and take them home no matter what."

Five months after she disappeared, Koharu's remains would be found floating in a bay near the mouth of the Kitakami River. DNA tests would confirm it was her.

Naomi Hiratsuka got her excavator's licence so she could search for her daughter, Koharu. ( ABC News: Mark Willacy )

"Finding her made a big difference to my husband and me. We could have a funeral and cremate her," Naomi said.

"She had come home to us."

Naomi Hiratsuka is just one of the incredible, indomitable parents I met during my coverage of the 2011 tsunami.

There was also Keitaro Fukuda, whose son and daughter also died at the Okawa school.

I first met him as he trawled through sodden debris next to the school oval, searching for any trace of his children.

They would eventually be found entombed in the mud.

There was Norio Kimura, who lost his father, his wife and his daughter Yuna when the tsunami thundered over the Fukushima coastline.

Norio Kimura shows a photo of his family as he searches for his daughter, Yuna. ( ABC News: Yumi Asada )

The seven-year-old remains the only person from their town still listed as missing. But Norio refuses to give up, regularly going into the nuclear fallout zone to search for little Yuna.

Initially he was searching alone but soon volunteers started joining him.

Norio Kimura is still searching for any sign of his daughter, seven-year-old Yuna (pictured). ( ABC News: Yumi Asada )

But because of the radiation, they are only allowed to search for five hours at a time.

Throughout the hours of searching, he has found things belonging to Yuna such as her clothing and shoes.

Norio has quickly built up a shrine of found belongings of his dead family.

"Yuna is not really here, but it's proof of her existence and that she was here," Norio said.

"And to feel that is the biggest joy for me now and it's a happy moment."

Norio Kimura has found clothing and shoes belonging to his family over the past five years of searching through rubble. ( ABC News: Yumi Asada )

His father's body was found inland not long after the tsunami, his wife's remains were found floating off the Fukushima coast weeks later.

Little Yuna is still missing.

More than five years on from the natural and nuclear disasters, their stories stay with me.

They are a reminder of the resilience and resolve of the Japanese people, and of the love and determination of parents faced with an unthinkable loss.

Watch Mark Willacy's documentary Fukushima on ABC iView.