This article originally appeared on VICE US.

The number of people infected by a pneumonia-like virus in China tripled over the weekend as authorities confirmed on Monday that the coronavirus had spread to many more regions and cities, including the capital Beijing.

With just days to go before hundreds of millions of people travel to celebrate Chinese New Year, the tripling of cases of the infectious disease has raised fears of a much wider outbreak, after the World Health Organization confirmed that the virus was being spread through human-to-human transmission.

Officials in Wuhan, where the outbreak of the coronavirus, 2019-nCoV, was first detected on December 30, reported 136 new infections on Saturday and Sunday, while authorities in Beijing and Shenzen confirmed a total of three cases on Monday, the first time infections have been reported outside of Wuhan in China.

Officials in Wuhan said 170 people remained in hospital, nine of them in critical condition.

Additionally, the coastal province of Zhejiang, which borders Shanghai, reported five suspected cases.

The Chinese government publicly acknowledged the crisis for the first time on Monday, with President Xi Jinping saying the outbreak needs to be “taken seriously,” adding that “party committees, governments and relevant departments at all levels should put people’s lives and health first.”

The World Health Organization said the spike in reported cases was “the result of increased searching and testing” for the coronavirus. In Wuhan, a third death linked to the virus was also confirmed over the weekend, with confirmed infections now totaling more than 200.

The Lunar New Year festivities take place next weekend and from Friday one of the largest mass migrations of humans on earth will begin. Wuhan is a critical rail hub for millions of passengers.

Authorities there have been screening people at airports and train stations for nearly a week and using temperature scanners in a bid to limit the spread of the disease.

The virus is thought to have originated at a seafood and meat market in Wuhan where wild animals are sold. While the WHO initially said there was no indication of human-to-human transmission, the organization updated its stance on Monday

“An animal source seems the most likely primary source of this novel coronavirus outbreak, with some limited human-to-human transmission occurring between close contacts,” WHO said on Twitter.

For weeks the identity of the virus remained a mystery, but scientists have now identified it as a strain of coronavirus that has led to an outbreak of viral pneumonia. However many aspects of the virus remain unknown.

The spread of the virus has brought back memories of the Sars virus — also a coronavirus — that killed 774 people in dozens of countries in the early 2000s.

As well as new cases in cities around China, there have also been cases reported internationally, in countries like Thailand and Japan. On Monday, South Korean authorities confirmed a woman who had arrived from Wuhan was infected.

On Friday, the U.S. began screening passengers coming from Wuhan and landing at airports in San Francisco, New York and Los Angeles.

“I think that this is a situation where we’re going to see additional cases all around the world as people look for it more,” Nancy Messonnier, director of the U.S.’ National Centre for Immunisation and Respiratory Diseases told reporters on Saturday, adding: “I think it’s highly plausible that there will be at least a case in the United States.”