Japanese police have blocked main roads in Tokyo during rush hour in an elaborate earthquake drill.

It is the first time the authorities have attempted to simulate the gridlock that would occur after a major disaster.

People across Japan hold drills every year on 1 September.

This year it has been taken even more seriously than usual because of the earthquake and tsunami that struck the north-east of the country in March.

At precisely 09:00 (00:00 GMT) sirens howled and whistles blew as the police stepped into roads and blocked them.

For 10 minutes traffic was stopped at 100 points in greater Tokyo, the biggest urban area in the world. Jams quickly built up.

The aim was to practise how emergency vehicles would get through the gridlock feared after an earthquake centred on the city.

Japan has been rehearsing for disaster on the morning of 1 September for years - it is the anniversary of a massive earthquake in Tokyo in 1923.

This is the first time traffic has been halted.

The decision was made after the earthquake and tsunami in March caused major disruption in the city, even though the epicentre was well to the north.

Schools and business across the country also practised evacuations.

And the cabinet held a simulated emergency meeting at the prime minister's office.

The elaborate drills, and an early warning system of loudspeakers, are credited with keeping the death toll in March below 16,000, with another 4,258 still missing.

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