Bad news, the pilot told us. There would be an emergency landing because of some mechanical problems, but there's nothing to worry about.

Sleepy and confused, we buckled up to land at the undisclosed destination. Some passengers on the half-empty flight struggled to see where they were. As the Boeing 777 glided smoothly onto the runway in the dark, the pilot announced: "Welcome back to Hong Kong."

All U.S. airports were closed following the terrorist hijackings and explosions in the United States on Tuesday, and this flight, after a departure from Hong Kong already delayed by seven hours, arrived back in Hong Kong at 4 a.m.

Some people chuckled, while others shook their heads in disbelief. At least one man cursed: "Seven hours' wait, seven hours in the air, back to square one." One flight attendant's eyes welled with tears when a passenger asked for details.

The Federal Aviation Administration ordered U.S. air space closed after the airborne attacks on New York and Washington. The FAA said the ban would not be lifted until noon Wednesday EDT at the earliest.

Security was heightened worldwide. Special police units patrolled airports in South Korea, the Philippines and elsewhere. Britain and Austria banned commercial flights over their capitals. Some airlines canceled flights to the Middle East. Israel closed its air space to foreign carriers.

Many airlines, including British Airways, Virgin Atlantic Airways, Belgium's Sabena, Air India and Hong Kong's Cathay Pacific Airways, canceled all Wednesday flights to the United States. British Airways also canceled flights to Islamabad, Pakistan's capital.

Closing U.S. air space forced diversions of hundreds of international flights - at least 40 flights were rerouted to Mexico City; 100 to Canada - leaving passengers stranded or diverted to airports hundreds of miles from their intended destinations. Tokyo's Narita International Airport expected to cancel 170 flights on Wednesday.

Others, like ours, just turned back.

"It's incredible to think that something like this can happen. I'm scared for myself, I'm scared for my family," American businessman Rich Schneeweis, 38, of River Vale, N.J., said at Hong Kong's airport after speaking by phone to his wife and two children, ages 4 and 8.

"I want to be with my family. Nothing else matters right now," said the stunned Schneeweis, who had been en route to Newark International Airport after a business trip to Hong Kong.

Passengers surrounded exhausted airport officials seeking details of the attacks.

"I guess I'm glad I'm safe, but sort of shocked. I'm going to go to the hotel and get some rest, do some e-mails, calls and let everyone know that I'm OK," said Jody Tjan, 30, a production manager from New York City.