Riot police preparing for a stand-off with protesters

The demonstrators had said they planned to block the delegates within the conference complex.

As we watched the riot police assemble behind their water cannon and armoured personnel carriers from our high-up hotel window, it began to look as if the protesters' way was firmly blocked.

But as the stand-off continued, more and more people, led by a few anarchists clad in black and bearing sticks, began to move around the building to find various weak points which had not been guarded by police.

Music and missiles

Things soon turned violent as anarchists began to tear down barriers near a rail line that runs under the road bridge.

Tear gas hangs over Prague

There was the repeated sound of tear gas being fired, and black smoke as riot police raced to the spot.

Soon there was also black smoke rising, as BBC camera crews filmed what appeared to be petrol bombs thrown by the demonstrators.

The air was filled with the sound of police helicopters, firecrackers, and ambulances, while the lone sound of a trumpet playing "We Shall Overcome" wafted over the proceedings.

Ring-side seat

A little later, demonstrators managed to penetrate within 100 yards of the Congress Centre itself by using a small tunnel under the rail line.

They occupied the Vysehrad metro station, which had been closed by the authorities for the day.

Some protesters daubed slogans on the station with spray paint while others shouted "fascist democracy" as another set of riot police moved smartly down the steps of the station.

Hundreds of delegates left the Congress to watch the proceedings from a bridge linking the conference centre to one of the main delegate hotels, the Corinthia.

They were soon to get an even closer view of the protests.

As we watched, another group of a few hundred demonstrators managed to reach that hotel, unnoticed by police.

Bystander hit

Led by a women dressed in bright feathers, and marching to the sound of drums, they advanced on the hotel before the outnumbered police made a stand on the Metro steps.

As delegates watched, some began throwing missiles, one of which hit a woman watching from the balcony.

As the riot police arrived, some demonstrators tried to overturn cars and waste bins to block their way.

But they were soon overcome, as the riot police charged and split them into small groups.

Several people, including at least one woman, were hit repeatedly by the police as they fell.

As the light began to fade, the protests appeared to subside, and it looked like the delegates would get home to their hotels in the evening.

But it was not quite so simple. The police opened the metro line, while keeping their barricades across the road bridge.

But as we boarded the train we discovered that it was not stopping in the city centre.

Instead, thousands of delegates were sent by buses from the end of the tube line to a heavily guarded assembly point, from where we eventually boarded another bus for the hotels.

As we sped through the deserted streets, it was clear that the protesters had proved once again that, despite their small numbers, they had been able to make an impact on the world stage.