Relatives of China's reformist premier have amassed huge riches during his tenure, according to a report Friday that came as the Communist Party prepares for a pivotal handover of power.

The New York Times investigation into the family of Wen Jiabao, who will be replaced in a 10-yearly leadership transition next month, came shortly before Chinese state media reported that a criminal probe had been opened into disgraced politician Bo Xilai.

Beijing immediately dismissed the NYT report as an attempt to tarnish China, with foreign ministry spokesman Hong Lei telling reporters in response to a question on the article: "Some reports smear China and have ulterior motives."

Detailing a string of deals, the newspaper said that many relatives of the government's number two -- a self-styled man of the people known popularly as "Grandpa Wen" -- had become "extraordinarily wealthy" during his time in office.

Investments by Wen's son, wife and others spanning the banking, jewellery and telecom sectors were worth at least $2.7 billion according to an analysis of company and regulatory filings from 1992-2012.

The revelations come as a particular embarrassment for Wen, who is the standard-bearer of the Communist Party's reformist wing and has campaigned against the rampant corruption that infuriates many ordinary Chinese.

In a speech published in April, he said official corruption was "the biggest danger facing the ruling party" and warned that "those who hold political power may perish" unless it is addressed.

President Hu Jintao, who like Wen will step down after 10 years in office, has also made fighting graft in the Communist Party a top priority, and the issue is sure to figure in the party's 18th congress starting on November 8.

Ahead of the congress, the party proceeded with an unfinished item of business Friday with the announcement by state media that ex-Chongqing city boss Bo had been expelled from parliament and his legal immunity lifted.

The decision to remove him from the National People's Congress cleared the way for Bo to be put on trial for corruption and other crimes related to the murder of a British businessman, with Xinhua later reporting that he was "under investigation for alleged criminal offences".

The State-owned news agency had said that Bo had "borne major responsibility" for the poisoning of Neil Heywood, even though his wife has already been convicted of his murder and handed a suspended death sentence.

Bo, who led a leftist "Red revival" inside the party from his base in Chongqing, was once tipped for elevation to the elite politburo and his demise has exposed internal divisions in China's highly secretive power structure.

The NYT investigation darkens the clouds hanging over the Communist Party caused by the Bo scandal as the regime prepares to name successors to Wen and Hu to steer the world's second-largest economy for the next decade.

Next month's congress will culminate in the unveiling of a new politburo that is expected to see Vice President Xi Jinping promoted to Communist Party general-secretary, in place of Hu.

Xi was the subject of a June investigation by financial news agency Bloomberg alleging that his relatives had also built up a giant portfolio of investments in property and stocks worth hundreds of millions of dollars.

Public anger about corruption and cronyism is on the rise in China, fanned by social media which enables the spreading of stories about official wrongdoing despite the best efforts of the country's powerful censors.

All online searches related to the New York Times as well as the newspaper's websites were blocked Friday, as were references to Wen, his wife and his son, Wen Yunsong.

The NYT investigation covered alleged dealings by Wen's younger brother and brother-in-law, as well as his businessman son -- one of the younger generation of so-called "princelings" with access to the upper reaches of the party.

The business of Wen's wife, Zhang Beili, a well-known jewellery and gemstone expert, had become "an off-the-charts success only as her husband moved into the country's top leadership ranks", The Times said.

His elderly mother meanwhile owned a stake valued at $120 million in 2007 in the enormous Ping An insurance giant, which benefited from reforms during Wen's tenure, according to the newspaper.

It gave no figure for the family's net worth now, but calculated the value of the assets they had controlled over the period examined. No holdings were found in Wen's name.

Speculation of a hidden fortune has been circulating for years, fuelled by US embassy documents from 2007 made public by WikiLeaks that alleged influence-peddling by members of Wen's family.

One cable suggested the 70-year-old leader knew of the business dealings of his family but disapproved of them.

The New York Times quoted one unnamed former government colleague of Wen who linked the report to the jostling for power inside the Communist Party, where former leaders retain influence after the end of their time in office.

"His enemies are intentionally trying to smear him by letting this leak out," said the former colleague.

A spokeswoman for the newspaper, Eileen Murphy, expressed disappointment that access to the company's English- and newly launched Chinese-language websites had been blocked as a result of the investigation.

The website of Bloomberg is still blocked inside China after its June expose on Xi.

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