The number of cases of COVID-19 has surged nearly 10-fold from the previous day in China’s Hubei Province, the epicenter of the outbreak. The number of new deaths also increased dramatically, to 242.

Officials explained the uptick Thursday by saying they had reclassified how they were diagnosing and counting cases of COVID-19. Health officials reported 14,840 new cases—reversing several days of declines in official new diagnoses in the province.

The new classification system of COVID-19 was meant to ensure that “patients can receive standardized treatment according to confirmed cases as early as possible to further improve the success rate of treatment,” according to the Hubei Province Health Commission.

The statement hinted that Hubei may have previously been under-counting the number of official cases of the coronavirus, adding that the change was “in order to be consistent with the classification of case diagnosis issued by other provinces across the country.”

Hours after the announcement of the spike in new cases, the Chinese government announced a political shakeup in Hubei. On Thursday, the Communist Party secretary of Hubei, Jiang Chaoliang, was removed from his post, according to state media. The mayor of Shanghai, Ying Yong, will replace him.

Jiang is the highest-ranking party official removed from office thus far over the outbreak. Public anger has swelled over the handling of the virus, and this week a petition calling on the national legislature to protect citizens’ free speech in China has gained momentum. The petition follows an outpouring of grief over the death of a young doctor who sounded the alarm on the virus and was punished by officials for speaking out.

Some experts say that it’s almost certain that the number of publicly confirmed cases is lower than the actual number of infections.

“Cases have definitely been underreported all along,” Charles Chiu, a professor of laboratory medicine at the University of California, San Francisco, tells TIME. Chiu says that there are myriad reasons for the undercounting, including delays in laboratory testing, a lack of standardization in diagnostic tests that can mean unreliable results and hospital capacity in Hubei.

“There have been reports of likely infected individuals being turned away from hospitals and sent home because the medical system in Hubei is being overwhelmed, with the focus on treating the more severely ill patients,” he says.

Ben Cowling, a professor of infectious disease epidemiology at the University of Hong Kong, tells TIME that he believes that one reason for the undercount is that China simply didn’t have the ability to test all suspected cases.

For that reason, he says it makes more sense to include those most likely to be infected in the official infection count, instead of only those cases that have been confirmed by a laboratory test.

“In SARS that’s what was done,” Cowling says. “In terms of monitoring the progression of the outbreak of infections, it’s quite a sensible idea to also report probable cases.”

The vice president of a Beijing hospital and one of the experts working on the coronavirus response told state broadcaster CCTV that the move is in line with China’s National Health Commission’s latest diagnostic guidelines, reports the South China Morning Post.

“When doctors diagnose pneumonia, they can only get the etiology of the disease 20 to 30 percent of the time. We have to rely on clinical diagnosis 70 to 80 percent of the time. Increasing the diagnosis of clinical cases will help us make an additional judgment on the disease,” Tong Zhaohui said, according to the Post.

On Thursday, officials in Hubei had reported just over 1,600 new cases—the lowest figure since the beginning of February. Experts said the declines were promising signals that China’s lockdown of tens of millions of people may be working to contain the spread of the deadly coronavirus.

It is not clear over what time period the newly announced cases were detected.

“I would like to know whether those 15,000 cases are recent cases, or they’re spread out over the last few weeks and this is somehow a backlog of cases that are now reported,” Cowling says.

Hubei, which includes the city of Wuhan—where the coronavirus is believed to have originated, has more than 80% of official cases worldwide.

Spotlight Story

What’s in a Name? Why WHO’s Formal Name for the New Coronavirus Disease Matters

The World Health Organization and public health experts agree COVID-19 is the best name for the disease

But experts say that the case count in the rest of China could still be much higher than reported. “It is unclear what the extent of diagnostic testing in China is outside of Hubei province,” Chiu says.

There are now more than 60,000 cases of COVID-19 worldwide, with all but about 500 in mainland China. There have been 1,367 deaths—with 1,310 of them in Hubei province.

Write to Michael Zennie at michael.zennie@time.com and Amy Gunia at amy.gunia@time.com.