Japanese tsunami survivors who were able to outrun the killer waves that raged out of the sea, have recalled how they saw those behind them consumed by the torrent of mud and debris.

Miki Otomo’s sister was one of the fortunate, though the image of victims violently swept away last week by the black tide of wrecked houses and cars near the hard-hit city of Sendai will be forever seared in her memory.

“My older sister was in a bus when the wave came behind them. The bus driver told everybody to get out of the bus and run,” Ms Otomo, a mother of three teens who herself managed to escape the deadly wall of water in her car, said.

“My sister was able to get away but some people just couldn’t run fast enough,” she said, adding they were engulfed by the swirling tsunami, which was sparked on Friday by a massive earthquake, the biggest ever recorded in Japan.

Ms Otomo, whose home near Sendai was destroyed in the twin disasters, says she quickly piled her father and her dog in the car in a desperate bid to survive. She is thankful that her entire family was able to escape the waves.

“The tsunami wave was coming and I grabbed grandfather and our dog and drove. The wave was right behind me, but I had to keep zigzagging around obstacles and the water to get to safety,” Ms Otomo said.

Ms Otomo is now living at an evacuation centre in an area school with about 1,000 other exhausted survivors who cheated death. Authorities fear that at least 10,000 people may have lost their lives.

In the gymnasium at the Rokugo junior high school, more than 100 people huddled in blankets on the floor as emergency food supplies were brought in.

Outside in the carpark, a water pump manned by volunteers provides a much-needed source of refreshment, local business owners arrive with crates of supplies, and a neat row of portable toilets has been set up.

At the entrance to the main hall, a neat arrangement of shoes is a testament to tradition, despite the disaster.

The atmosphere is strikingly calm, orderly and determined.

Maki Kobari, an English teacher, said she and her colleagues at the school – a designated emergency shelter – raced to help shortly after the tsunami hit.

They spent the first night after the catastrophe in the classrooms with only a few crackers between them.Some people are still too shocked to express the terror of their ordeal, let alone face the uncertainty of their future, Ms Kobari explained.

“Some people lost their whole families, they lost everything,” she said.

Apart from a violent fissure in the carpark, there are shockingly few visible signs of the utter devastation less than a mile away, where the once suburban landscape is empty and eerily silent.

Cars were tossed across the muddy wasteland like dice – one was awkwardly balanced on top of another, while around five vehicles had washed up within the walls of a house compound.

The roof of one house, apparently shorn from the building, lay on the waterlogged ground. A fridge and a sofa also were pitched incongruously in the mud.

Groups of emergency crews in orange jumpsuits picked through the vast fields of rubble. Army trucks and police rescue vehicles drove into the disaster zone, although tsunami warnings pushed them back at least twice on Sunday.

Farmer Yoichi Aizawa, 84, said he had briefly returned to his house to retrieve some of his belongings, but cannot imagine when – or if – he will be able to go home again.

“When the earthquake occurred, the house was OK so I thought it was going to be alright,” he said.

“But when the waves came, that was unexpected. The wave was the most scary thing.”

Factbox

Following is a background on events at the Fukushima plant in northeastern Japan, crippled by the tsunami:

Nuclear power

A nuclear reactor produces electricity from pellets of enriched uranium that fit into fuel rods. The energy from nuclear chain reaction heats water, producing steam to drive turbines which in turn produce power. The rods are encased in a steel reactor vessel, which in turn is protected by a containment vessel, essentially a thick shell of reinforced concrete designed to prevent any radioactive gas or material from escaping.

Earthquake procedures

Friday’s tsunami caused an automatic shutdown at Fukushima, in which the fuel rods dropped into the reactor shafts to stop chain reaction. However, the rods continued to emit large amounts of residual heat, which had to be dissipated by water circulating within the reactor vessel. The problem is that the main cooling system at the No. 1 reactor failed, as did a backup system. Operator Tokyo Electric Power took the drastic measure of using sea water to try to cool the reactor.

Causes of the blast

On Saturday, an explosion at the No. 1 plant blew apart the building housing the reactor, although Tepco says it did not affect the steel reactor vessel itself. They say the blast was chemical, not nuclear, and was probably caused when the very high temperatures in the reactor produced hydrogen from the water, causing the flammable gas to build up.

What if a meltdown occurs?

A “meltdown” occurs when fuel rods melt at extremely high temperature, which has the potential to cause an explosion that breaches the reactor and spews radioactive material into the air. The Japanese government says it is highly likely that a partial meltdown occurred at the No. 1 reactor, but without a reactor breach. A partial meltdown may also have occurred at the No. 3 reactor.

Is the situation similar to Cheronbyl?

The April 1986 blast at Chernobyl, caused by a reckless experiment, was the worst nuclear accident in history. But the Soviet power station had no containment vessel, which meant that a vast amount of radioactive debris was released into the air and blown across parts of Ukraine, Belarus and western Europe. Japan’s nuclear safety agency so far rates the Fukushima accident at four on an international scale from 0 to 7. The 1979 Three Mile Island accident in the US was rated five, while Chernobyl was a seven.

What about danger to health?

The authorities say some radioactive vapour was intentionally released to ease pressure on the No. 1 plant and some contaminated vapour was emitted in Saturday’s explosion. The government says none of the releases has reached levels high enough to affect human health. (Sources: Jean-Mathieu Rambach, expert at the French Institute for Radiological Protection and Nuclear Safety; Olivier Gupta, director of Nuclear Safety Authority; Bertrand Barre, scientific advisor of nuclear engineering group Areva; US Nuclear Regulatory Commission; AFP news reports).