HONG KONG (REUTERS, BLOOMBERG) - Hong Kong health authorities on Wednesday (Jan 5) began a citywide search for the contacts of a Covid-19 patient and ordered a Royal Caribbean "cruise to nowhere" ship to return to port early as health officials feared a fifth wave of infections.

One government Covid-19 adviser told local media he estimated there were up to 10 invisible transmission chains in the community and along with two other expert advisers urged the government to tighten restrictions. 

The global finance hub has stuck to a zero-Covid-19 strategy by largely isolating itself from the world and enforcing a stringent and costly quarantine regime.

On Dec 31, a streak of three months without community cases ended with the first local transmission of the new Omicron variant.

Since then, the authorities have scrambled to track down and test hundreds of people who had been in contact with a handful of Omicron patients.

"The most stringent anti-epidemic measures will be implemented to prevent the mutant strains from spreading in the local community," the government said in a statement.

The latest hunt was sparked by a patient who danced with some 20 friends in a central park on New Year's Eve. Two of the fellow dancers, one of whom was a domestic helper, came up positive in preliminary Covid-19 tests.

The helper’s employer and eight other of her close contacts then went on a cruise journey on Jan 2.

As part of its coronavirus restrictions, Hong Kong has restricted cruises to short trips in nearby waters, with ships asked to operate at reduced capacity and to only allow vaccinated passengers who test negative for the virus.

The Spectrum of the Seas ship had about 2,500 passengers and 1,200 staff on board. The nine close-contact passengers were isolated from the rest of the people on board, and preliminary tests taken during the journey returned negative results, the authorities said.

"Spectrum of the Seas is taking appropriate measures under guidelines by the Department of Health," Royal Caribbean told Reuters in a statement.

The nine close contacts will be sent to a quarantine centre, while the rest of the passengers and staff will have to undergo several compulsory tests in coming days, the government said.

Additionally, people who have been to 47 places across Hong Kong around the same time as the close contacts of recent patients have been issued compulsory testing notices, the government said in a separate statement.

The venues include the central Victoria Park, the newly opened M+ modern art museum, ferry piers, restaurants, retail stores, clinics and others.

Dr Gabriel Leung, University of Hong Kong (HKU) dean of medicine and a government adviser, told public broadcaster RTHK there were probably "five-to-10 invisible transmission chains" in the city.  

"There’s no time to waste," Dr Leung said. "We need circuit-breaker measures."

Two other advisers, Dr Yuen Kwok-yung and Dr Ivan Hung, said officials should consider closing schools and curbing restaurant hours, local media reported. 

Separately, Hong Kong is rushing to plug holes that have seen the Omicron finally break through the city’s defences, banning five more individual airline routes – including those from Seoul, Vancouver and Delhi – after discovering infected passengers.

Embattled flag carrier Cathay Pacific Airways as well as Air India, Air Canada, Thai Airways International and Philippines AirAsia have had routes suspended from Tuesday to Jan 17, the government said. That was the most flights Hong Kong has banned in a day since Omicron emerged in November last year.

In total, the authorities have banned 24 routes in less than six weeks, throwing holiday travel into chaos. 

Cathay is bearing the brunt of Hong Kong’s strict Covid-19 countermeasures as it is based in the Asian financial hub, which is pursuing a Covid-Zero strategy that is increasingly strained as Omicron spreads around the globe, accounting for the majority of new infections.

The airline has had seven routes suspended since Christmas Day, including London, Los Angeles and San Francisco.

The latest ban is for Cathay’s Seoul services after three passengers tested positive on arrival from the South Korean capital on Jan 2.