China has pledged a "thorough" probe of sensational allegations of abuse of power and murder involving a disgraced leader, indicating it would deal harshly with those found responsible.

The case of politician Bo Xilai, a rising star who had seemed destined for the apex of the Communist leadership, has rocked China since he was dramatically ousted this month in a move that exposed frictions at the top.

Bo, the boss of the southwestern metropolis of Chongqing, was sacked from the post and stripped of his elite position in the Communist Party, while his wife has been placed under investigation for the murder of a British national.

A commentary by the official Xinhua news agency released on Wednesday said the government would "thoroughly investigate related events."

It added that the mysterious death of Briton Neil Heywood was "a serious criminal case involving the kin and aides of a party and state leader."

The commentary, almost certainly approved at the highest level of the government, appeared to suggest authorities would make examples of those involved to counter what it described as a worsening rot in governance.

"The party is... being confronted with the danger of a slackened spirit, incompetence, divorced relations from the people, inactivity and corruption," it said.

"Those in power should be concerned about and held responsible for the results of their usage of power," it added.

Heywood was found dead in a Chinese hotel room in November in what was initially blamed on excessive alcohol consumption.

But the case took a shocking turn last week when Xinhua announced Bo's wife Gu Kailai was being investigated for alleged murder.

The Xinhua commentary came after British Prime Minister David Cameron on Tuesday offered to help in the probe into Heywood's death.

The offer was made during a meeting at Downing Street with visiting senior Chinese Politburo official Li Changchun.

Bo, the son of a revered communist revolutionary, had launched a draconian crackdown on criminal elements in Chongqing and a "red revival" campaign marked by the mass singing of old Maoist-era songs.

Many analysts saw the moves as a bid for entry to China's inner circle.

The ruling party will complete a once-a-decade power transition later this year centering on a new line-up for the powerful nine-member Politburo Standing Committee that governs China and which Bo was widely tipped for.

But the rapid unraveling of his fortunes has exposed a harsh factional pushback against the charismatic and ambitious Bo, and the affair has been seen as a huge embarassment for the party.