The best way to describe it was a rumble. The hotel building didn't sway. The mirror didn't fall off the wall. But the after-shock was making its presence felt. The powerful vibration continued for a minute or so and then subsided. While there have been 150 after-shocks since the earthquake, this was my first experience. The eerie feeling happened again two hours later. It's unnerving.
I arrived in Tokyo late last night, with camera operator Pol Reygaerts, after being scrambled from Brussels. We made our way into the busy Shinjuku district to see how people are coping. The skyscrapers draped with neon signs were bright as ever. The fashion conscious were out in style.
But things have changed.
Put simply - people are concerned: concerned for the people still missing from the tsunami but also concerned about the danger posed by radiation from the Fukushima nuclear plants.
Official statements are confusing the public. They're being told that the legal limit for radiation - 500 micro sieverts - was exceeded overnight. (The peak was 1,204.) At the same time, officials declare, there's no threat to human health. How can that be, people ask, when the same officials say the emergency cooling system at Fukushima Reactor 3 has failed and there's a risk of an explosion?
Trying to get anywhere near the plants - if you wanted to go - is nigh impossible for anyone other than emergency services. The famous bullet trains, many of which hug the eastern coastline, have been cancelled. Local trains are severely curtailed. Main highways are being limited to vehicles involved in the emergency response. There are road-blocks on some national roads. Flights to near-by towns are booked out.
Pol and I decided on another route - fly to the north of Japan and then make our way down towards Sendai, the worst affected area by last week's tsunami. On a sunny Sunday morning, we made our way through the capital's spectacular city centre to Haneda Airport and flew to Hakodate, and then took a ferry across Mutsu Bay to the city of Aomori.
Our original aim was to make it to Yamagata tomorrow where we could travel onto the devastated Sendai district. However, after considering the issue of radiation, and ongoing problems with the nuclear reactors, we decided against it. Instead we've reached Misawa on the upper North East Pacific coastline. UK rescue teams landed tonight at the US base and the area will be used for missions further south. Misawa was affected by the tsunami itself - dozens died here.
The earthquake which caused the horror struck so violently has now been upgraded to a 9.0 scale tremor. Some say it's the 5th most powerful earthquake in 100 years.
Japan has now mobilised a 100,000-strong Self Defence Force to help clean up and provide assistance to survivors. It's the biggest mobilisation since World War 2. Tonight, in a prime time address to the people, the Prime Minister used the war analogy himself - saying Japan faces its greatest crisis since that immense conflict.
This evening the police suggested that as many as 10,000 people may have died as a result of the earthquake and tsunami. However it's still uncertain - one coastal district, which has a population of 9,500, is still 'missing' presumed lost. The toll is going to rise significantly.
Another unknown is what precisely is going to happen at the Fukushima nuclear plants. This morning 210,000 were being evacuated from the 20 kilometre emergency zone. Now the figure is put at 350,000. Latest reports say seawater is being poured into a 3rd reactor in a desperate move to prevent it overheating and going into meltdown.
When the radiation headed to more than twice the legal limit overnight, people in danger were instructed to close windows and doors; cover the mouth and nose with a wet towel and cover-up as much as possible.
Unsurprisingly - people right across Japan are worried. That's as true in Sendai as Tokyo as Misawa. Just as I finish writing, a second aftershock in ten minutes has rumbled underneath me.
Worrying times indeed.
