Full body searches are being carried out on all those flying to the United States from Hong Kong - and controversial X-ray-like body scanners may be on the way amid heightened security fears.

The new "full pat-down" searches and extensive carry-on luggage checks by airline staff follow a security directive issued by Washington in the wake of the failed Christmas Day "underwear bomber".

Officials at Chek Lap Kok insist the checks - which take place immediately before boarding - will not add journey time for passengers.

The United States singled out 14 "high-risk" nationalities for the checks but Hong Kong has decided to search everyone, regardless of nationality, both for logistical reasons and to avoid accusations of discrimination.

It is also looking at introducing controversial scanners that are capable of peering through clothes to create three-dimensional images of passengers to reveal any concealed weapons or explosives. Authorities in Britain, Canada, the Netherlands and Nigeria have faced a public backlash over the scanners amid privacy fears.

Sidney Chau Foo-cheong, the executive director of Avseco, Chek Lap Kok's security provider, said the 14 high-risk countries are Afghanistan, Algeria, Cuba, Iraq, Iran, Lebanon, Libya, Nigeria, Pakistan, Saudi Arabia, Somalia, Sudan, Syria and Yemen.

But Chan added: "It is very difficult to separate them and it will be very bad in terms of discriminating against people and delaying them.

"It is difficult in Hong Kong and it is also manpower intensive to separate these nationals. Therefore, the airlines have decided that they will conduct 100 percent pat-down searches of everyone."

He said there have been no complaints from passengers so far. "We explain to them it is for their own safety. The passengers in general don't welcome it but they understand the situation."

The searches are conducted at the entrance to the airbridge near the boarding gate or on the airbridge itself.

It means all passengers on the nine daily flights to the United States will undergo two security checks, one after clearing immigration, and the new one.

A spokeswoman for Airport Authority Hong Kong (AAHK) said: "Hong Kong International Airport (HKIA) maintains its general security measures while respective airlines operating flights to the United States will conduct extra body and baggage searches in front of the boarding gates."

Among the carriers who fly stateside from Hong Kong are American Airlines, Delta Air Lines, Cathay Pacific Airways, Continental Airlines, United Airlines and US Airways.

On December 25, Umar Farouk Abdulmutallab, 23, tried to bomb Northwest Airlines Flight 253 from Amsterdam to Detroit by detonating explosives hidden in his underwear. The device failed, only setting off a fire in his seat.