A brother of China's former internal security chief Zhou Yongkang has been detained by investigators, state-controlled media reported Monday, after a government spokesman declined to deny the retired political heavyweight was under investigation.

Zhou Yuanqing and his businesswoman wife Zhou Lingying were taken away from their home in Wuxi in the eastern province of Jiangsu on December 1 by "discipline investigators from Beijing", the Beijing News said.

The husband is a brother of Zhou Yongkang, according to the report, who amassed huge power during his time as China's security chief and retired as a member of the Communist Party's all-powerful Politburo Standing Committee (PSC) in late 2012.

The wife was a major investor in a multi-million-dollar Audi dealership and her success "had a lot to do" with Zhou Yongkang's son Zhou Bin, the newspaper added.

She was also involved in a liquefied natural gas station partnership with a company affiliated to state-owned China National Petroleum Corp., the oil giant once headed by the politician.

Rumours have been circulating for months that Zhou Yongkang is being investigated for corruption.

At least six high-ranking officials believed to have been his proteges have fallen since the once-in-a-decade power transition that anointed Xi Jinping as the ruling party's general secretary.

The New York Times in December cited "sources with elite political ties" as saying that Xi had given the go-ahead for the investigation of Zhou.

It would be the first time in decades that such a high-ranking figure has been targeted in a formal inquiry, and would send shockwaves through China's elite. PSC members have generally been regarded as untouchable even after retirement.

On Sunday, a spokesman for the Chinese People's Political Consultative Conference, a debating chamber that is part of the Communist Party-controlled governmental structure, avoided denying that Zhou was under investigation at a press conference.

"We mean it when we say anyone will be seriously investigated and severely punished as long as he violated the party's disciplines or the country's law, no matter who he is or how high-ranking his position is," Lu Xinhua said in reply to a question about Zhou's status.

"This is all that I can say to answer your question. You know what I mean," he said, provoking laughter from journalists.

Chinese authorities normally rush to deny accusations against Communist Party leaders.

The Global Times newspaper, which is close to the ruling party, on Monday ran a commentary saying that Lu's answer suggested investigators were still probing Zhou.

"The investigation obviously is not completed yet and so probably there is no conclusion that can be announced to the outside world," said the article bylined Shan Renping, believed to be a pseudonym used by the newspaper's senior editors.