Hong Kong leader Carrie Lam declared a virus emergency on Saturday, announcing measures to limit links with mainland China and prevent the spread of the new coronavirus.
Flights and high speed rail trips between Hong Kong and Wuhan, the epicentre of the outbreak, will be halted. Schools that are currently on Lunar New Year holidays will remain closed until Feb. 17 and education authorities have asked universities to extend leave for students.
Hong Kong's health authorities have confirmed 5 coronavirus cases, all linked to Wuhan, with a further 122 people being treated as suspected of having the disease.
Lam said all official visits to the mainland and official Lunar New Year celebrations would be scrapped immediately. But she rejected calls for a temporary ban on all arrivals from the mainland and said it would be impractical to shut down all border crossings with the mainland.
Lam also said she had sought assistance from China's State Council to ensure there were adequate supplies of masks.
Lam is dealing with the health issue as she faces broader tensions after seven months of sometimes violent anti-government protests.
"I hereby urge all citizens stay united to fight against the epidemic to protect all Hong Kong people's health and safety," she said.
The demonstrations have centred on Hong Kong's relationship with mainland China: some protesters have railed against growing interference from Beijing while others have expressed concern over greater integration with the mainland.
Beijing denies meddling and blames the West for stirring trouble in the former British colony.
Lam, speaking hours after returning from the World Economic Forum in Davos, insisted Saturday's announcement was not delayed due to her trip, saying she had stayed in close touch with officials while in Switzerland.
The first case in Hong Kong of the new coronavirus was confirmed on Wednesday, a 39-year-old man visiting from Wuhan who crossed by high-speed rail from neighbouring Shenzhen.
The condition of one of the people confirmed with the virus deteriorated on Saturday and the patient was now on a respirator, Hong Kong's government funded broadcaster RTHK reported.
Hong Kong earlier deployed temperature screening equipment at the airport and the high-speed rail station. Air and train passengers are required to fill in health declaration forms at the border while isolation wards have been set-up in hospitals.
Many people are using masks in offices and on public transport, a reflection of the city's strong memories of an earlier coronavirus crisis.
Gabriel Leung, the dean of the medical school of Hong Kong University, urged the public to increase its already-substantial wearing of glasses.
“The short-sighted rate in Hong Kong is the highest in the world. So, mostly everyone has small protection - glasses," he said, urging others to wear glasses too.
"This is not a perfect measure, but can let you prevent from the droplet transmission to a certain extent," Leung said.
Coronaviruses are a family of viruses named because of crown-like spikes on their surfaces. The viruses cause respiratory illnesses ranging from the common cold to the deadly Severe Acute Respiratory Syndrome (SARS).
Hong Kong was badly hit by the SARS virus in 2003 and has had many episodes of H5N1 bird flu for more than a decade. According to WHO figures, 1,755 people in Hong Kong contracted the SARS virus at the time and 299 died.