The billionaire said no one had tried to blackmail him and he had not been involved in any disputes before the ram-raid attacks on the group's headquarters and two hotels and vandalism at 16 mobile phone shops on Wednesday and Thursday.

Commenting on whether a rental dispute with tenants in one of his shopping malls in Tsim Sha Tsui might have triggered the attacks, he said: 'We get along well. This should not be linked.'

Describing himself as, 'of course, a bit unhappy', he said: 'I really don't know why this happened. It appears they want to challenge the police.'

Mr Cheng said he would co-operate fully with police in their investigations. 'I hope the police will find the truth,' he said.

He also insisted the attacks had not affected his group's operations.

While Mr Cheng professed himself unconcerned, New World has heightened security for the tycoon, his family and the group's properties.

'More bodyguards have been deployed to protect the chairman,' a source in the group said.

A security guard was standing guard outside the main entrance of the group's headquarters in Queen's Road Central. Police also have stepped up patrols around all New World-related properties, including the chairman's home.

A police spokesman refused to comment on whether the tycoon had been placed under round-the-clock police protection.

But an unmarked police car with two plainclothes officers was seen guarding the entrance of Mr Cheng's home, and uniformed police arrived to make checks every hour before dawn yesterday.

The spokesman said police were investigating the motive behind the attacks. 'We are looking into all possible clues,' he said.

So far no one has been arrested.

Speaking in Beijing while attending a donation ceremony yesterday, New World Development managing director Henry Cheng Kar-shun said the company had checked everything but could not work out a motive for the attacks. 'Personally, I haven't offended anyone. So there will not be any problem with my personal safety,' he said.

Between 5am and 7am on Wednesday, 16 mobile phone shops run by New World Mobility were daubed with paint and a stolen car was rammed into the main entrance of the New World Renaissance Kowloon Hotel in Tsim Sha Tsui.

The following day a car was reversed into the main entrance of the JW Marriott Hotel in Admiralty at 5.45am. Minutes later, a car, believed by police to be the same one, was reversed into the back entrance of the New World Tower office complex in Central.

New World Development is one of Hong Kong's largest developers.