The World Health Organization said Hong Kong's anti-coronavirus efforts in the past six weeks were "very effective".

Michael Ryan, executive director of WHO Health Emergencies Program, made the remarks at a news conference on the novel coronavirus in Geneva on Monday. He said Hong Kong did well in both suppressing and driving down transmissions.

Addressing the same conference, WHO Director-General Tedros Adhanom Ghebreyesus said almost nine times as many coronavirus cases were reported in the last 24 hours outside the Chinese mainland than on it, where the number of newly reported cases is declining.

The world is in "uncharted territory" on the coronavirus outbreak as the escalating epidemic worsened in Iran, South Korea and Italy, but the chief remained optimistic about halting the spread.

"There is no choice but to act now," he said.

Stringent measures

Stringent measures have been taken in Hong Kong to contain the spread of the disease. The SAR government successively closed down all but three border checkpoints; it also imposed a 14-day mandatory quarantine on every arrival from the mainland.

Meanwhile, it requires visitors from South Korea, three Italian regions and Iran to be quarantined for 14 days amid the rising numbers of infections in those places.

The government also set up a HK$30 billion (US$3.9 billion) fund to give the city's coronavirus-stricken industry sectors a boost.

Hong Kong had confirmed 100 cases of infection as of Tuesday. Chief Executive Carrie Lam Cheng Yuet-ngor said before the weekly Executive Council meeting on Tuesday the situation was  controllable, "but we still need to stay alert because the coronavirus has no borders".

Reducing the spread from outside is vital, but it is also important to prevent the city experiencing a mass community transmission, Lam said.

The government has been looking for more quarantine facilities to accommodate possible visitors from high-risk countries such as Iran and Italy. A total of 118 new units inside the Lei Yue Mun Park and Holiday Village were completed in less than a month, and will start operating in two weeks.

Lam called on members of the public to understand and support the government's moves to set up more quarantine centers and coronavirus clinics.

"We can only win this fight against the coronavirus when everyone stands in solidarity and lends a helping hand," she said.