'I heard screaming and came outside,' he said. 'The police came immediately. Then armed police in black uniforms and helmets arrived and took charge. They pulled everyone out and shut the area down. I saw blood on the ground in the Drum Tower compound.'

A German tourist reached the scene before Benoit.

'I saw a guy lying at the bottom of the Drum Tower,' the German said. 'The police came put a black blanket on his body. Then they erected a fence.'

Both refused to give their full names because of concerns about their visas.

Many tourists watching the Games, sightseeing and shopping, could not believe that it had happened in Beijing, a city protected by more than 110,000 police.

Chris Rice, an American who arrived in Beijing last month, said he was shocked. 'I thought that if something happens it should be a terrorist attack with a bomb or something,' he said. 'I could never have imagined an ordinary Chinese guy would stab foreigners so brutally.'

Mr Rice said he had been in Wangfujing, the shopping district, with thousands of Chinese watching China's basketball team playing against the US a few days ago.

'People booed when the US team scored,' he said. 'There were so many people there that for once I was afraid something might happen. But I have never been pushed around or attacked. And later people cheered when the US team scored. I have not had any unpleasant experiences since I came.

'But I would definitely be more careful when I'm walking on the street from now on.'

Although most people were astonished, not everyone was worried about the city's safety.

Ulrich Heegaarp from Denmark said the incident would not change his perception of the city and its people. 'I am not afraid at all because I know the nature of Chinese people. They are gentle,' Mr Heegaarp said. 'Such an incident could happen anywhere in any country.'

But condemnation quickly surged in mainland chat rooms. In Hangzhou , where the attacker came from, netizens accused him of tainting the national pride that many Chinese felt after the opening event.

'It is a shame for Hangzhou, a shame for China and a shame for the world,' one contributor said.

Attacks on foreigners on the mainland are rare, but a Canadian model was murdered last month in Shanghai and a tour bus carrying Australians was hijacked in Xian , Shaanxi province , in March by a man who was later shot in the head by a police sniper.

The Drum Tower, used by emperors to mark the hour, is north of the Forbidden City. Built in the 13th century, it is one of the oldest buildings in Beijing.