THEY were flying a remote- controlled toy helicopter right next to a sign banning the activity.

When Hong Kong man Law Kwok Wah, 44, asked his friend to pass him the controls of his toy, tragedy struck.

The blade from the 1.5m-long helicopter struck him in the head, causing a 20cm-long gash to the back of his head, reported TheStandard.

He was rushed to Queen Elizabeth Hospital and underwent emergency brain surgery.

The 6kg helicopter belonging to one of Mr Law's friends - a 1.5m-long SST Eagle 3 WC worth about HK$30,000 ($5,500) with accessories - had just touched down with its rotor still spinning, reported The South China Morning Post.

It is suspected one of the controls was accidentally pressed when the friend, surnamed Wong, handed the radio controls to MrLaw. This caused the helicopter to suddenly move forward, its spinning rotor slamming into MrLaw's head.

Police said the accident happened close to 2pm on Sunday when Mr Law and his friend were flying a remote-controlled helicopter at an open space on Chun Wang Street in Tseung Kwan O.

Police said the man was a friend of the toy's owner.

Mr Law had apparently asked to try the toy and accidentally hit a button on the remote control, causing the helicopter to crash into his head.

The blades of the helicopter broke off in the accident.

Police are still investigating. The Civil Aviation Department said it will follow up the case, adding that licensing is not required for helicopters weighing less than 7kg.

The accident happened at a government site with a warning sign prohibiting flying remote-control toys.

But some say they simply ignored the warning due to lack of other places in urban districts for their activities.

A man known only as Mr Tong told The Standard that there are about 50,000 to 80,000 players in Hong Kong.

Mr Tong said there is only one official site in Hong Kong to fly toy helicopters and the lack of sites makes it difficult. Because of signal interference, only one at a time can send his toy aircraft aloft.

Mr Kenny Ma, chairman of the Hong Kong Radio Control Soaring Society, said he had known MrLaw for many years and he was an experienced model flyer.

FIVE YEARS' EXPERIENCE

'I have known him for some years. He has over five years of experience of flying both radio-controlled soaring planes and micro-radio-controlled helicopters,' he said.

People new to flying model aircraft might have poor safety awareness, but Mr Law would not be one of them.

Fans of model planes said they suspect the accident could have been caused by a disruption in radio frequency.

'Sometimes different people may unknowingly be tuned to the same frequency to control their craft,' one said.

The HK Aviation Department said they would investigate the accident and follow up if necessary.