The Chinese doctor who first sounded the alarm about the coronavirus died Thursday from the disease, his friends and colleagues said.

Li Wenliang, 34, was an ophthalmologist at Wuhan Central Hospital. Wenliang was arrested on January 1, after attempting to share information on the coronavirus. It was well before Chinese health authorities revealed its full threat. Two days prior to his arrest, Li attempted to warn his medical school colleagues about the existence of a contagious new virus that resembled the lethal severe acute respiratory syndrome (SARS).

Li’s message began to spread across China, but his posts were censored by the government and he was detained for “rumor-mongering.” Instead of listening to his warnings, Chinese Communist authorities arrested him and forced him to write a “self-criticism,” a method of punishing dissenting voices.

The Washington Post reports that after arresting Li, Wuhan police went on Chinese state television to warn the public to not spread rumors. In conjunction with state media, they urged Internet users across the country to not believe online rumors and help build a “clear and bright cyberspace.”

On December 31, the Chinese government informed the World Health Organization’s China office of the mysterious diseases’s presence in Wuhan. However, it took weeks for Chinese health officials to acknowledge the severity of the outbreak. Then, they began to quarantine tens of millions of people in Wuhan and surrounding areas.

As of Tuesday, more than 23,500 cases of coronavirus were confirmed worldwide, with at least 490 deaths in China alone. The vast majority of the infections, and all but two of the deaths, are in mainland China.

Wuhan Mayor Zhou Xianwang has said the efforts to contain the virus are “severe and complex” as the number of confirmed cases grows. There is also concern over a shortage of medical supplies and masks. is continuing to monitor the coronavirus worldwide.