A burst of shots rang out suddenly, sending a crowd of young protesters charging down the Calle Septima, the main street running through the centre of Bogotá. The students were followed by ranks of riot police dressed in full black body armour. Ahead of them another wave of police arrived on motorbikes, brandishing machine-guns. The students, trapped between the two, raised the chant: "Fuera Bush! Fuera Bush!"
In the distance, imposing black tanks lined the side of the road. Tear gas drifted on the breeze, making our eyes water and our throats itch. The protesters, many of whom are students aged 16 or 17, scattered, lobbing rocks at the police as they went.
Despite the presence of the police and army, they caused extensive destruction. Every one of the many large banks and offices lining the street had their glass fronts smashed. The pavements were covered with broken glass. Chairs were dragged out on to the street and set alight. Anti-imperialist graffiti was daubed across every shop front.
A group of riot police was resting by the side of the road, their black uniforms spattered with red paint. "It's blood - one of them stabbed me in the back," joked one, with a tired smile. His colleagues, who looked as young as the protesters, didn't laugh. Each one had his blood type carefully printed in red on his helmet.The protesters were high on adrenalin and full of rage, directed as much towards Colombia's president, Álvaro Uribe, as towards the president of the United States.
"We are protesting against both of them, since Uribe just does what Bush wants," said Andrea Suarez, a 17-year-old student from the Colombian National University. "They want everything in Colombia to be privatised. They want to privatise our universities, and we won't be able to pay. They don't respect the rights of indigenous people, and they don't think about the poor."
"Bush is like an emperor . . . the head of an imperialist government," said Wilder Romero, 24, a street vendor. "He is only coming here to see what he can take away. And our government is completely allied with him."
The protests that greeted the first visit of a US president to Colombia since Kennedy may have been violent, but thanks to the extreme security measures taken by the Colombian government they were limited and mainly involved a small hard core of left-wing students, some of whom carried posters of Mao. The authorities had made clear that no kind of major protest would be tolerated: most of the main streets of the city were closed off, and the public universities - centres of radical politics - were shut down. The area surrounding the Palacio de Narino, where Bush was received, was sealed completely. Riot police and army waited on every corner, most shops were closed, and the sale of alcohol was banned.
"Everyone would like to protest, but there is lots of repression here, and everyone is scared," said Jorge Suarez, a kindly looking middle-aged salesman. "It is the wrong moment for him to come here. He has committed barbarities all over the world."
Official sources estimated that up to 2,000 had participated in the protests: 127 people were detained by the police, 25 of whom were under 18 years old.
Colombia, responsible for 90 per cent of the world's cocaine trade, receives more US aid than any country outside the Middle East and Afghanistan.