Beijing (AFP) - The number of people infected in China by the coronavirus outbreak jumped on Wednesday to nearly 500, after Hong Kong reported its first death from the disease and millions more in China were ordered to stay indoors.

The confirmed toll in mainland China rose to 490 after hardest-hit Hubei province reported 65 more people had died -- the biggest single-day tally since the first fatalities emerged last month.

More than 20 countries have confirmed cases of the virus, prompting the World Health Organization (WHO) to declare a global health emergency, several governments to institute travel restrictions, and airlines to suspend flights to and from China.

The WHO said Tuesday that the dramatic measures taken by China had provided a "window of opportunity" to halt transmission, while calling for more global solidarity to combat the virus.

The novel coronavirus has continued to spread with Singapore, Malaysia, and Thailand on Tuesday reporting new infections that were not imported from China.

In a sign of growing concern about a spread to other densely-populated Chinese metropolitan areas, authorities in three cities in eastern Zhejiang province -- including one near Shanghai -- limited the number of people allowed to leave their homes.

Three districts in Hangzhou -- including the area where the main office of Chinese tech giant Alibaba is based -- now allow only one person per household to go outside every two days to buy necessities, affecting some three million people.

The city is only 175 kilometres (110 miles) southwest of the financial hub of Shanghai, which has reported more than 200 cases, including one death.

Zhejiang has confirmed 829 cases -- the highest number outside the central province of Hubei, whose capital Wuhan is the epicentre of the outbreak.

The disease is believed to have emerged in December in a Wuhan market that sold wild animals, and spread rapidly as people travelled for the Lunar New Year holiday in January.

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China has struggled to contain the virus despite enacting unprecedented measures, including virtually locking down more than 50 million people in Hubei.

The WHO has said the outbreak does not yet constitute a "pandemic".

The head of the organisation, Tedros Adhanom Ghebreyesus, accused wealthy countries of falling short on their duties in sharing data, stating that: "Of the 176 cases reported outside China so far, WHO has received complete case report forms for only 38 percent."

- Hong Kong's first death -

The death of the 39-year-old man in Hong Kong came as the semi-autonomous city closed all but two land crossings with the Chinese mainland.

Hong Kong media said the man had underlying health issues. He had visited Wuhan last month and his 72-year-old mother was also infected.

The financial hub has been particularly on edge over the virus as it has revived memories of the Severe Acute Respiratory Syndrome (SARS) outbreak of 2002-03, which killed nearly 300 people in the city and 349 people in the mainland.

Health officials noted that the mortality rate for the new coronavirus stood at 2.1 percent, with most victims either old or with underlying health problems.

SARS killed nearly 10 percent of patients.

- New foreign cases -

Singapore confirmed the first four cases of people being infected locally, taking the total number of infections in the city-state to 24.

In another example of growing global anxiety, Japan has quarantined a cruise ship carrying 3,711 people and was testing those onboard for the virus after a former passenger was diagnosed with the illness in Hong Kong.

Macau, China's semi-autonomous gambling hub that is popular with mainland Chinese visitors, decided to temporarily close all of its casinos for at least two weeks.

And the UK Foreign Secretary Dominic Raab on Tuesday advised Britons to leave China, "if they can", to minimise their risk of exposure to the virus.

The United States, meanwhile, acknowledged that the outbreak may delay Beijing's plans to purchase American goods under the terms of a deal meant to end the two countries' trade war.

- Beijing admits 'shortcomings' -

China's Communist leadership made a rare admission of fallibility earlier this week, acknowledging "shortcomings and difficulties exposed in the response to the epidemic".

The elite Politburo Standing Committee called for improvements to the "national emergency management system" at the meeting, according to the official Xinhua news agency on Monday.

The government also said it "urgently" needed medical equipment such as surgical masks, protective suits, and safety goggles as it battles the outbreak.

Most of the deaths have been in Wuhan and the rest of surrounding Hubei province, which has largely been under lockdown for almost two weeks.

A 1,000-bed field hospital in Wuhan built from scratch within two weeks to relieve overburdened medical facilities started receiving patients on Tuesday, with a second makeshift hospital due to open later this week.

A cultural building, an exhibition centre and a gymnasium have also been converted into improvised clinics with 3,400 beds.

State media reported that the city planned to convert an additional eight facilities into hospitals.

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