An American tourist has been stabbed to death and his wife seriously injured in an attack in Beijing that has cast a shadow over the city's hosting of the Olympic games.

The Chinese attacker killed himself shortly after the incident on Saturday, jumping to his death from the historic Drum Tower, a popular tourist spot, China's official Xinhua news agency reported on Saturday.

The agency did not give any motive for the attack.

The American killed in the attack has been named as Todd Bachman, the father-in-law of the US men's volleyball coach, the US Olympic committee said in a statement. His wife is being treated in intensive care in a Beijing hospital.

The Chinese capital has been quiet in the run-up to the Olympics, with security tight across the capital and thousands of security officials patrolling the streets and the games venues, but some small-scale protests have persisted.

Tibet protest

Protesters staged a mock 'die in' in Tiananmen Sqaure on Saturday [EPA]

"The Chinese government is seeking to cover up its ugly occupation of Tibet with the bright lights of the Olympics," Matt Whitticase, a spokesman for the group, said.

"Our action at Tiananmen Square today highlights the determination of Tibetans and people of conscience that no amount of repression from the Chinese government will extinguish the desire of Tibetans for freedom and to speak out against China's worsening abuses in Tibet."

The protesters - from the US, Germany and Canada - staged a "mock die-in" on the north side of the square.

Police detained them about 10 minutes into the demonstration, the group said.