China has blocked internet searches for the term "body double" amid rumours that the wife of fallen political star Bo Xilai used a stand-in during her murder trial.

Chinese state television on Monday showed a brief clip of Gu Kailai standing in the dock as she was handed a commuted death sentence for the murder of British businessman Neil Heywood.

But her appearance, looking notably plumper than in earlier photographs that have appeared in foreign media, sparked suspicions that the woman in court might actually have been someone else.

Some overseas Chinese websites even alleged the person who appeared in court was a woman called Zhao Tianshao, from northern China's Langfang city.

China's censors moved quickly to muzzle the rumours and on Wednesday the term "ti shen", or body double, remained blocked on many popular websites in the country.

A search for the combined terms "ti shen" and "Gu Kailai" on Baidu, the top search engine in China, returned a line saying "part of the search results are not displayed according to relevant laws and policies".

Sina Weibo, a Chinese microblogging service similar to Twitter, blocked any postings that mentioned "ti shen".

It is not the first time that a high-profile defendant has been accused of using a stand-in in China.

In 2009 there were suspicions that the son of a wealthy businessman, who ran over and killed a young man, had used a stand-in at his trial, after he appeared noticeably heavier than in pictures taken at the scene of the accident.

China's state-run media have stuck to official accounts of the Gu murder case, which brought down her husband, a former Communist party leader and reformist mayor of one of China's biggest cities, and rattled the Communist hierarchy ahead of a handover of power due to start later this year.

ABC/AFP