Via the BBC:

On Tuesday, [journalists in China for the Olympic Games] were unable to access the website of Amnesty International as it released a report criticising China’s human rights record.

Some international news pages and sites that dealt with issues such as Tibet were also inaccessible, journalists said.

As the BBC explains:

China enforces tough internet controls, but said when it bid for the Games that journalists would be free to report.

And the IOC’s attitude? International Olympic Committee press commission chairman Kevan Gosper confirmed that this had at least in part been agreed to by the IOC when he said that,

Some of the IOC officials had negotiated with the Chinese that some sensitive sites would be blocked.