But no takeover was happening. This was just the normal show of force of Tokyo's Metropolitan Police Department (MPD), famed for making the streets of the Japanese capital the safest in the world.
In the past nine months the city's police have been more evident than ever, with a couple of sensitive visits by the Emperor to China and Okinawa, followed by the Crown Prince's wedding of last week, and the forthcoming summit of the Group of Seven leading industrial nations in Tokyo next month. In each case extreme left- and right- wing terrorists have threatened to let off bombs and rockets in the capital, keeping the police on their toes - and visible on the streets. Last week the police announced they had found material for eight bombs stored in a greengrocer's shop linked with a left-wing group.
There are sporadic complaints that the efforts of Tokyo's finest to provide security are sometimes excessive and intrude on individual liberty. But, in general, Tokyo residents are prepared to tolerate a certain level of intrusiveness from the police in exchange for the feeling of safety that has long since disappeared from the streets of Western capital cities.
The real value of Tokyo's security sinks in when one travels from Tokyo to London to find friends who are afraid to go anywhere at night, who have bars on all their windows, who tell stories of pensioners being beaten for a few pounds of savings, and whose lives are severely compromised by the real threat of mugging or rape in the streets ouside their houses.
Tokyo is not like this. 'People from overseas often praise us for being the safest city in the world,' said Tadao Ando, the superintendent general of Tokyo Metropolitan Police. 'From the statistics, you can see it is the kind of city where you can walk alone at night.'
According to the National Police Agency, for every 100,000 inhabitants, Japan has 1.1 murders, 1.3 (reported) rapes, and 1,203 incidents of theft. The comparable figures for England and Wales are 9.1 murders, 12.1 rapes, and 5,544 incidents of theft. And if a crime is committed, the chances are much higher that the police will make an arrest in Japan than in the UK.
While some overworked policemen in London might resign themselves to just signing-off a burglary report for insurance purposes, for his counterpart in Tokyo it is almost a matter of personal honour to make an arrest. Seventy-seven per cent of burglars and 93 per cent of murderers are caught. 'Our men have high morale and high capability,' Mr Ando said. 'I do not think I am bragging about this.'
On top of this, Mr Ando has a co- operative public. 'Citizens in general consider discipline as part of the Japanese nature. They are highly law- abiding and trust the police force.'
Vandalised telephone boxes are unknown in Japan. As Sir John Whitehead, a former British ambassador to Japan put it, with 2 per cent unemployment, 'the real achievement of the Japanese system is that people feel they have something at stake in their society'. There is virtually no alienated underclass.
There is a cost for Tokyo's safe streets. Policemen visit every home on their beat at least once a year - more often if they have suspicions about the residents - to keep tabs on what everyone is doing. If an arrest is made, the suspect can be detained for questioning at the police station for three weeks; two days is normal for most developed countries. Stories of beatings, sleep deprivation and forced confessions are common: Japanese citizens know that if they fall out of the system, they will be treated with little compassion.
But with a continual stream of horror stories of Japanese being attacked or robbed while abroad being relayed by television and newspapers, most Japanese are grateful for their domestic security.
There has been criticism within Japan of the heavy police presence on the streets at this year's big events, and the police have acknowledged this. But Mr Ando is unapologetic for carrying out his duty. 'When I wake up in the morning my first question is: 'Has anything happened last night?' When I hear nothing has happened I am very relieved.'