Chinese government censors have launched a sweeping campaign to purge any mention of a corruption investigation in Namibia from the internet because it involves a company formerly run by the son of China's president.

The government's Central Propaganda Department has ordered all Chinese search engines to block any searches related to the case and has also shut down popular social networking sites such as Facebook, YouTube and Twitter.

The crackdown came after African media reported three people had been charged with corruption in connection with a lucrative contract for Nuctech, the airport scanner company controlled by Hu Haifeng, the 38-year-old son of President Hu Jintao.

The reports said Namibian prosecutors had travelled to Beijing to request that Mr Hu be interviewed in relation to the case but not as a suspect.

A spokesman for the European Commission said yesterday that the EU was also investigating claims Nuctech engaged in unfair trade practices through the use of soft government loans to secure contracts in Europe. The investigation is not related to the Namibia case.

Chinese internet searches for information on either case yesterday were blocked or turned up the message: “According to relevant laws, regulations and policies, some search results have not been displayed.”

The corruption allegations, although not levelled at the younger Mr Hu, will be acutely embarrassing for China's president and the Communist party, which has made battling corruption a centrepiece of this administration.

Regular campaigns are launched against corrupt cadres, with heavy sentences ranging from long jail terms to the death penalty.

Corruption among senior leaders and their privileged relatives is an explosive issue that has often stirred rebellion in China and was a core complaint of protesters in the 1989 Tiananmen Square demonstrations.

Namibian prosecutors are accusing three men, including a Chinese citizen identified as Nuctech's Africa representative, of arranging a bribery scheme to help secure a $55m contract to install Nuctech scanners at ports and airports across the country.

The contract was signed in May last year, around the time Mr Hu was promoted from president of Nuctech to become Communist party secretary of Nuctech's parent Tsinghua Holdings, a state-owned company attached to the elite Tsinghua university where both Mr Hu and his father studied engineering. The company was unavailable for comment yesterday.

The Namibian government agreed to pay $12.8m of the contract but the three men named in the case allegedly took nearly half of that money and went on an alleged “spending spree”, according to an affidavit from Namibia's Anti-Corruption Commission cited in media reports.

The rest of the contract was to be paid using soft loans from China's state-owned Export and Import Bank on condition the contract went to a Chinese company.

Nuctech is owned by the state and controls around 90 per cent of the domestic Chinese market for x-ray scanners at airports and ports.

The very existence of senior government leaders' family members is considered a state secret in China.