The stakes are high for China to pull off a trouble-free G20 summit of the world's top economies, its highest profile event of the year, as it looks to cement its global standing and avoid acrimony over a long list of tensions with Washington. Shortly after Obama's plane landed in the eastern city of Hangzhou, a Chinese official attempted to prevent his national security adviser Susan Rice from walking to the motorcade as she crossed a media rope line, speaking angrily to her before a Secret Service agent stepped between the two.

Rice responded but her comments were inaudible to reporters standing underneath the wing of Air Force One. It was unclear if the official, whose name was not immediately clear, knew that Rice was a senior official and not a reporter. The US aide insisted that the journalists be allowed to stand behind a rope line, and they were able to record the interaction and Obama's arrival uninterrupted, typical practice for U.S. press travelling with the president. A White House spokesman and China's Foreign Ministry both did not respond immediately to requests for comment.

The altercation occurred out of sight of Obama, who greeted ambassadors and other officials before the presidential motorcade pulled away with Rice. The incident is an illustration of the image-conscious ruling Communist Party's efforts to control the media as its seeks to orchestrate what it hopes will be a flawless event. China has taken extensive security measures in preparation for the G20 summit opening on Sunday.

On Saturday, many roads and shops in Hangzhou were deserted and shuttered in the usually bustling city with a population of 9 million. The Chinese government has broad control over domestic media and prevents many foreign media outlets from publishing in the country, including by blocking their websites.

Obama has raised issues of freedom of the press on previous visits to China, which insists that media must follow the party line and promote "positive propaganda". Foreign reporters are often physically prevented from covering sensitive stories, but altercations involving foreign government officials are rare. Rice met Chinese dissidents before her last trip to China in late July, when she held talks with President Xi Jinping and other senior officials.

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