A?sex scandal in the southwestern city of Chongqing which led to the downfall of 11 high-level officials may not yet be over.

A whistleblower says he has video footage of more officials, all holding higher ranks than Lei Zhengfu, the sacked Party secretary of Beibei District who was the first to come under the spotlight.

Zhu Ruifeng says the videos show at least five more officials having sex with women hired by developers intending to use blackmail to secure construction deals, the Qilu Evening News reported yesterday.

Yesterday, police questioned Zhu for seven hours about the tapes and said he could be liable for prosecution if he did not surrender them, according to The Associated Press.

"The police were very polite but they said they wanted the videos. I firmly refused because I have to protect my source," said Zhu, who said he was interviewed by Chongqing officers. "They threatened me with the law, saying I could be accused of concealing evidence."

Zhu said the questioning followed a late-night visit by two police officers to his home in Beijing on Sunday.

Police are entitled to question a witness and request evidence, one of Zhu's lawyers, Li Heping, said. But Zhu also had the right to refuse in order to protect his source.

Local authorities haven't confirmed the existence of the five officials, but Zhu said that if they tried to shield them, he wouldn't hesitate to post the tapes online.

A woman said to be involved in the scandal, Zhao Hongxia, is being held by police, Zhu quoted police sources as saying.

She is said to have been filmed with at least six of the 11 officials sacked after the scandal broke and one of three women hired by the Chongqing Yonghuang Group to lure officials into having sex, the newspaper reported.

Chongqing police have not confirmed Zhao's detention. "We will report to the public if we make progress in the investigation," an officer told the newspaper.

The scandal emerged in November after a video featuring a Chongqing official, later confirmed as Lei, went viral online.