A journalist with China's official Xinhua news agency on Wednesday accused the head of a key state-owned firm of "corruption involving a huge amount".

The allegations -- in the form of an open letter to the ruling Communist Party's disciplinary department -- come as China's new leaders repeatedly pledge to stamp down on graft.

But within hours of Wang Wenzhi detailing his allegations on China's Twitter-like Sina Weibo, his account was blocked and could no longer be accessed.

Xinhua's own website itself carried a report on his posting, but then took it down.

Chinese authorities have in some cases encouraged whistle-blowers to reveal alleged corruption, but have also sometimes cracked down on them.

Wang accused Song Lin, chairman of China Resources (Holdings) Co, of losing the firm billions of yuan (hundreds of millions of dollars) in a deal to buy assets from another company.

"Song Lin and other senior managers who participated in the acquisition neglected their duty and are suspected of graft involving a huge amount," Wang wrote.

Wang said he was compelled by his "sense of responsibility and conscience as a Chinese citizen and journalist" to report the scandal, adding he would publish more evidence later.

"I am very well aware of the huge risks this reporting under my real name could bring to my family and myself in current China," he wrote in the posting.

"But I firmly believe that there is justice in China under the leadership of the party."

China Resources agreed to buy several mining and factory assets in 2010 from a private company in the northern province of Shanxi for 7.9 billion yuan ($1.3 billion), Wang said.

Some key price assessment reports were provided by an agency hired by the seller, he added.

A previous potential bidder had estimated the same assets to be worth just 5.2 billion yuan, Wang added.

The licences of some of the coal mines which China Resources bought expired and production was suspended even before the purchase, according to Wang, with one now being used by farmers to graze their sheep.

China Resources, a Fortune Global 500 company, is a conglomerate operating in sectors including retail, property, finance and electricity.

Company representatives were not immediately available for comment.

The company reports directly to the central government, making Song's position equivalent to a vice-minister, according to Chinese media reports.

The allegations come after unrelenting anti-corruption rhetoric by the country's leaders in recent months, with President Xi Jinping warning graft could "destroy the party" and threatening "no leniency" for those involved.

Liu Zhijun, the former rail minister, was given a suspended death sentence -- normally commuted to life in prison -- this month for bribery involving at least $10.5 million, the highest-ranking official punished for corruption since the new leadership came into office.

Several other senior figures have come under investigation, including Liu Tienan, former deputy director of the top economic planning agency, and senior provincial officials.

Allegations against Liu Tienan surfaced when a journalist at the influential business magazine Caijing accused him online of improper business dealings late last year.