A Hong Kong cruise ship carrying 3,700 people was ordered back to port on Wednesday for virus testing after nine people were found to be close contacts in an Omicron variant outbreak.
Like mainland China, Hong Kong pursues a zero-Covid policy and maintains some of the world's strictest measures -- including virtually closed borders, weeks-long quarantines, targeted lockdowns and mass testing.
The city has recorded 114 Omicron cases, with the vast majority identified at the airport or during the 21-day hotel quarantine that is mandatory for most arrivals.
But a small community outbreak traced to Cathay Pacific airline staff has sparked mass testing and contact tracing in recent days.
On Wednesday, those tracing efforts reached the "Spectrum of the Seas", one of the vessels offering cooped-up Hong Kongers a "cruise to nowhere" that sails into international waters for short trips.
Health authorities said nine people on the cruise, which left on Sunday, were classified as close contacts and ordered the ship back to port a day early.
All on board -- 2,500 passengers and 1,200 crew -- must test negative before they can disembark.
An AFP reporter outside the cruise terminal on Wednesday could see guests relaxing and exercising on their outdoor balconies.
"A lot of dining tables and seats in the theatre were sealed, and we have wristbands that can help track our movements on board," one passenger on board, who asked for anonymity, told AFP by phone.
"When we booked the tour we knew there was a risk. It's just unlucky that it's us," she added.
Microbiologist Yuen Kwok-yung, one of Hong Kong's top Covid-19 experts, warned that an invisible infection link might have formed in the city.
"The fifth wave is very likely to take place," Yuen told reporters on Tuesday.
Hong Kong's strict health rules have kept the city largely free of the virus, with just over 12,000 cases and 213 deaths since the pandemic began.
But it has also left a business hub that dubs itself "Asia's World City" cut off from the rest of the world, including mainland China.
Hong Kong leader Carrie Lam has said that resuming travel routes with mainland China must come before reopening to the rest of the world.
But earlier this week she said the latest outbreak would likely delay those plans.
International businesses have voiced growing frustration with Hong Kong's global isolation as they struggle to retain and recruit talent as rival financial hubs learn to live with the virus.
Multiple airlines have begun avoiding Hong Kong and pulling out pilots and crew from the city.
Hong Kone carrier Cathay Pacific has dramatically slashed passenger and cargo flights in recent weeks because of tightened quarantine measures.