BEIJING—A newly identified virus originating in central China has spread to South Korea, killed a third person in China and reached at least three more population centers within the country, as the number of live cases has more than tripled—a major escalation in the outbreak of the pneumonia-like disease.

South Korean authorities confirmed Monday that a 35-year old Chinese woman who had flown into the country from the Chinese city of Wuhan, had contracted the novel coronavirus, part of a class of pathogens that can cause…

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