Cambodia declared its first case of coronavirus on Monday, as US President Donald Trump said America would offer any help to China over the continued spread of infections. The Cambodian Health Minister, Mam Bunheng, said on Monday that a Chinese man, who came with his family from the central Chinese city of Wuhan, the origin of the outbreak, to the coastal city of Sihanoukville this month had fallen sick but was stable. A second case was also confirmed in Canada, after the wife of the first coronavirus patient tested positive at a public health laboratory, the province of Ontario's Health Ministry said on Monday. The patient has been in self-isolation and is being monitored, the ministry said. "From what we know, Wuhan novel coronavirus transmits through close contact, and there's no closer contact than between a husband and wife," Ontario's Health Minister, Christine Elliott, said on Twitter. The new flu-like virus has killed 81 people, all in China, and infected more than 2,700. More than a dozen countries have reported cases so far. Mr Trump tweeted that the US offered China any help necessary and "our experts are extraordinary". The US has five confirmed cases of the virus. China on Monday further expanded its efforts to contain the deadly virus, extending the Lunar New Year holiday to keep the public at home and avoid spreading infection as the toll rises. Mongolia closed its vast border with China, and Hong Kong and Malaysia announced they would bar entry to visitors from the Chinese province at the centre of the outbreak, after a warning by medical officials that the virus’s ability to spread was growing. Travel agencies were ordered to cancel group tours nationwide, adding to rising economic losses. Stock markets around the world were down sharply on Monday as the lockdown in Chinese cities was expected to stifle travel, shopping and business for millions of people. The end of the Lunar New Year holiday, China’s busiest travel season, was pushed back to Sunday from Thursday to “reduce mass gatherings” and “block the spread of the epidemic”, a Cabinet statement said. The government of Shanghai, a metropolis of 25 million people and a global business centre, extended the Lunar New York holiday by a week within the city to February 9. It ordered sports stadiums to close and religious events to be cancelled. Tens of millions of people in China and around Asia had been due to crowd into planes, trains and buses to return to work after visiting their hometowns or tourist sites for the holiday. Hubei province, where includes Wuhan, has had 76 deaths reported so far. There have been one each in Shanghai and the provinces of Hebei in the north, Heilongjiang in the north-east and Henan in central China. The spread of the illness is being watched around the globe, with a small number of cases appearing in other countries. South Korea confirmed its fourth case on Monday. Cases also have been confirmed in Thailand, Taiwan, Japan, Vietnam, Singapore, Malaysia, Nepal, France, Canada and Australia. The US cases are in Washington state, Chicago, southern California and Arizona. China also reported eight cases in Hong Kong and five in Macao. Dr Chuang Shuk-kwan, head of Hong Kong’s communicable diseases branch, said the city’s eight cases all have Hubei ties, so there was no sign yet that it is spreading to the general population. Mongolia is the second country to close its border with China, following North Korea. Neither has reported any cases of the virus. Mongolia also closed its schools, universities and playgrounds for more than a month. The Potala Palace in Lhasa, the Tibetan capital, closed indefinitely to tourists on Monday. The former imperial palace in Beijing closed on Friday until further notice and other major tourist sites also have shut down, including two of Hong Kong’s most popular tourist attractions, Hong Kong Disneyland and Ocean Park.