Chinese health officials said on Tuesday that the death toll from an outbreak of a new form of coronavirus has climbed to six as authorities attempt to contain the disease's spread.

Reuters reported that the updated total comes as new cases were reported Monday in Guangdong province, in Beijing, and in new areas of the country where they had not been reported before, including two cases in the northern city of Tianjin, nearly 12 hours away from Wuhan, where the outbreak began.

Health officials also said on Monday that the first human-to-human transmission had been confirmed, though such cases are still rare.

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“The recent outbreak of novel coronavirus pneumonia in Wuhan and other places must be taken seriously,” Chinese President Xi Jinping said Monday. “Party committees, governments and relevant departments at all levels should put people’s lives and health first.”

Additional cases of the disease, thought to have originated in a now-closed seafood market in Wuhan, have also been reported in Thailand and the Philippines as authorities in neighboring countries scramble to locate Chinese tourists who have possibly contracted the disease. The virus, a recently unknown form of coronavirus, is thought to cause a deadly form of pneumonia.

China's health commission warned this week that the exact cause of the virus remains unknown, and encouraged local health officials to collaborate on containment efforts.

“However, the source of the new type of coronavirus has not been found, we do not fully understand how the virus is transmitted, and changes in the virus still need to be closely monitored," the commission said.