By Rupert Wingfield-Hayes
BBC News, Tokyo
Normally crowded platforms on Tokyo's subway system are at times near empty
As overseas governments accelerate efforts to evacuate their nationals from Japan amid strong warnings about the radiation dangers from the Fukushima Daiichi nuclear plant, Tokyo feels eerily quiet.
The sky is clear and blue. From my hotel window the late winter sunshine glints off the snow-capped perfection of Mount Fuji.
This being Japan, no-one is running around screaming and shouting.
The streets are quiet and orderly - but life here is definitely not normal.
The threat to Tokyo's 30 million people is invisible. Everyone is now asking themselves the same question.
When does the crisis unfolding at the Fukushima nuclear plant 150 miles (240 km) to the north cross that invisible line when you decide the risk of staying here is too high?
For many with young children that line has already been crossed. You can see them at Tokyo station with pushchairs, dashing to get on a bullet train to Osaka.
And beneath the surface veneer of calm and order there are signs of a society in deep shock and filled with anxiety.
I have been coming to this city at least once a year for the last 18 or so. Ever since I met a young Japanese woman and decided I wanted to marry her.
Tokyo has always been a place of wonder and fascination.
On a normal day Tokyo can make any other city in the world feel grey and boring.
The streets pulse with neon 24 hours a day. In Harajuku you can stare in wonder at the young boys and girls dressing up as Japanese cartoon characters, the girls in frilly miniskirts, their faces painted white and their heads crowned with bright blonde hair.
At way past midnight you can sip an ice cold beer and eat the best sushi in the world at a little place near Ginza station.
The famous neon signs of Tokyo have been turned off to conserve energy
And, yes, you really can see besuited office workers, known here as "salarymen", fast asleep on the pavement after a heavy night drinking with clients and missing the last train home.
If I had not been here in normal times I might have missed the small but significant changes.
Fewer people are walking the streets. The traffic jams are gone. Face masks are now worn by almost everybody.
The neon lights have been switched off, and restaurants are now closing at 10 if they are open at all.
And behind the public facade - the outward face that Japanese people are trained to put on from childhood - there is fear.
Inside their homes people are glued to the television, watching the events at Fukushima with growing dismay. What seemed to be a serious but manageable crisis a few days ago has grown and grown.
But the understandable fear of what might happen at the Fukushima plant is overshadowing the real human tragedy unfolding further north along the devastated coastline.
We have all now seen the extraordinary TV pictures of the tsunami rolling in. They are like a scene from a far-fetched Hollywood disaster movie.
There is a voyeuristic compulsion to watch them over and over, and a danger of forgetting that the pictures are of real towns, populated by real people, thousands of whom are now dead or missing.
Japan is usually a very easy place to get around. You can hop on a bullet train in Tokyo and be 300 miles away in less than two hours.
But now just getting to the disaster zone is a gruelling 11-hour drive on tiny back roads through the mountains. When you get there you enter another surreal world.
In Miyagi prefecture we drove towards the coast through beautiful picture-postcard countryside. Little valleys filled with rice fields surrounded by mountains and bamboo forests.
The fishing port of Kesennuma is a vast debris field that was once a town
Nothing seemed out of place. No sign at all of damage from the massive earthquake.
Even as we approached the little fishing port of Kesennuma there was no hint of what we were about to find.
Then as we crested the last ridge before the coast the world changed. In front of us lay a vast debris field that had once been the town.
Everything was destroyed. Houses smashed to pieces, others still intact, but lying on their roofs like some tortoises.
Cars, crushed beyond recognition, littered the landscape.
As we drove down into the port, the scene became even more unreal.
As I rounded a corner I was confronted by a 10,000-tonne ship sitting perfectly upright in the middle of the road.
On the day I was in Kesennuma they brought only two people out of the destruction alive. All the rest were bodies.
Like the tsunami that hit South East Asia six years ago, the division here is between those who escaped the wave and survived, and those who did not and died.
For those who did survive there is no end in sight to the suffering.
Yesterday in Tokyo I met a group of young British teachers who had just been evacuated from the disaster zone.
They were visibly upset at leaving behind Japanese friends and students, and irritated that we all seem more concerned about the nuclear power plant.
Please tell the outside world that the people up in the north need our help, they said, they do not have enough to eat, they are cold and in shock - they need help.
It is an extraordinary thing to say about one of the richest countries in the world.
But the scale of this disaster is so vast that even wealthy, advanced Japan is struggling to cope.
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