A top official linked to one of China's most powerful politicians has been placed on leave for stress, the government said Wednesday, amid speculation that he had tried to flee the country.

Wang Lijun, vice mayor and former police chief of Chongqing, is famed as one of China's top graft-busters after leading a crackdown that led to scores of senior officials being jailed in the southwestern city of 30 million people.

He has close links with Chongqing's Communist Party secretary Bo Xilai, who is the son of a Chinese revolutionary and is widely expected to be promoted to a top party post in a 10-yearly leadership transition that begins this year.

Wang was dismissed as Chongqing police chief last week, and on Wednesday, Chinese websites buzzed with rumours he had sought asylum at the US consulate in the southwestern city of Chengdu.

The Chongqing government refused to comment when contacted by AFP, but a posting on an official microblog said Wang was on sick leave -- a term often used as a euphemism for a political purge in China's one-party system.

"Due to long-term overwork, a high level of mental stress and physical exhaustion, Vice Mayor Wang Lijun is currently receiving vacation-style treatment following approval," the provincial government said Wednesday.

China's Internet authorities have censored microblog postings and searches using Wang's name, although news websites widely carried the government statement.

The US embassy in Beijing refused to comment on rumours of an asylum request, which comes at a sensitive time with China's vice president and leader-in-waiting Xi Jinping is due to make an official visit to Washington next week.

"I am not in a position to comment on issues regarding reported requests for asylum," embassy spokesman Richard Buangan told AFP.

"We cannot comment on issues regarding the security of diplomatic facilities," he added when asked about reports of an increased police presence at the Chengdu consulate.

Calls to Chengdu police went unanswered Wednesday.

As Bo's right-hand man, Wang, 52, an ethnic Mongolian, gained national fame while toppling former city deputy police chief Wen Qiang in a massive crackdown. Wen was executed in 2010.

The crackdown led to the arrest and detention of dozens of triad bosses and hundreds of their protectors in government and the police.

According to the Hong Kong-based Information Centre for Human Rights and Democracy, Wang's dismissal as Chongqing police chief was approved by China's highest ranking law official Zhou Yongkang.

Zhou is a member of the party's politburo standing committee, China's leading decision-making body that is made up of nine top officials and headed by President Hu Jintao.

Wang's boss Bo has long been seen as a contender for a seat on the committee later this year when seven members -- including Hu, Zhou and Prime Minister Wen Jiabao -- will step down, making way for a new generation of leaders.

Known as a "princeling" due to his father's revolutionary legacy, Bo has encountered opposition from those against nepotism and hereditary rights in China's political system.

At the same time, Bo's crackdown on corruption in Chongqing was widely popular, although responses to his campaign to instil "red" or communist-style patriotism in the municipality were mixed.