Hong Kong (CNN) The number of novel coronavirus cases has risen to more than 64,000 worldwide, after China reported another major increase at the epicenter of the outbreak following a change in how authorities there diagnose cases.

As of Friday morning, over 100 more people had died of the virus, officially known as Covid-19, in central China's Hubei province -- raising the global death toll to 1,383. Of those, all but three have died in mainland China.

Chinese health authorities also confirmed an additional 5,090 cases across the country. That's a major spike, but nowhere near the 14,840 new cases reported Thursday -- the largest single-day rise since the epidemic began.

The government explained the spike was due to a change in how cases are tabulated -- the total will now include "clinically diagnosed cases" -- people who demonstrate all the symptoms of Covid-19 but have either been unable to access a test or are believed to have falsely tested negative. The hope is that more people will be able to receive treatment by receiving this diagnosis.

The health system in Hubei, particularly in the capital Wuhan where the outbreak began, has struggled to handle the influx of patients, even with the help of several purpose-built hospitals dedicated to treating Covid-19. Provincial authorities said there are about 37,000 patients in hospital, 1,685 of whom are in critical condition.

More than 6,723 patients in China have recovered and been discharged since the outbreak began.

Beijing purge

As the number of deaths and cases at the epicenter of the outbreak continued to rise, China moved to purge several officials in the region, replacing them with loyalists of Chinese President Xi Jinping, who has now taken personal charge of the response.

State media announced Thursday that the Communist Party chiefs of Hubei and Wuhan had both been removed. Ying Yong, the former mayor of Shanghai, will become the new Hubei chief, while Wang Zhonglin will take over Wuhan itself. Ying is a key protege of Xi's, and the two men have worked together since the early 2000s when they were both officials in the eastern province of Zhejiang.

Another Zhejiang veteran and Xi ally, Chen Yixin, is already in Wuhan. Chen arrived in the city last week to lead the response to the epidemic -- his appointment there was seen as Xi moving to take charge of the crisis after it was mishandled in the early weeks by Wuhan and Hubei officials, who have been accused of downplaying the severity of the virus, resulting in its spread nationwide.

The removal of the Wuhan and Hubei party chiefs might only be the beginning of the provincial purge. Last week, amid nationwide outrage over the death of whisteblower doctor Li Wenliang -- who was reprimanded for spreading "rumors" by Wuhan police -- Beijing dispatched an anti-corruption team to the city to investigate the matter.

Wuhan Mayor Zhou Xianwang, one of the public faces of the crisis, previously offered to resign "to appease public indignation," but the central government has yet to take him up on that.

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Worldwide spread

While the vast majority of Covid-19 are in mainland China, the virus has been confirmed in more than two dozen countries worldwide , and concern is growing over its potential spread outside the epicenter.

"This outbreak could still go in any direction," World Health Organization director general Tedros Adhanom Ghebreyesus said Wednesday

"We have to invest in preparedness," Tedros said, adding that richer countries should help invest in countries with a weaker health system. He warned the virus could "create havoc" if it reaches a country whose health system is not capable of handling such an epidemic.

Three additional cases were confirmed in Hong Kong as of Friday morning, bringing the total to 53 in the semi-autonomous Chinese city, which has been in partial shutdown for weeks and closed most of its borders with the mainland. One of the three deaths outside mainland China occurred in the city.

The third of those deaths occurred in Japan on Thursday -- a woman in her 80s, according to health officials. She was not a passenger on board the Diamond Princess cruise liner currently quarantined at Yokohama, south of Tokyo.

The ship is currently home to the largest outbreak outside mainland China. Another 44 cases of the virus were confirmed Thursday, bringing the total of cases on the ship to 219, as Japanese health authorities continue to test the more than 3,500 people on board.

Japanese health minister Katsunobu Kato said that people who had tested negative for the virus and were over 80 years old, or had a non-virus medical condition requiring attention, would be allowed to leave the ship and move to a government medical facility. He did not give a timeline for that process. Already on Tuesday, an unknown number of passengers with non-virus medical conditions had been allowed to disembark.

Frustration is growing, however, among the thousands passengers and crew on board, who have been unable to leave the ship for a week now.

Speaking to CNN, one crew member said she feared the crew were at greater risk of being exposed to the outbreak because they were not being quarantined in the same way as the passengers and were having to continue working to take care of the guests.

Sonali Thakkar, 24, from Mumbai, said she and her colleague -- who she shares a cabin with -- became ill with a headache, cough and a fever two days ago. Her supervisor told her to stop working and she is currently staying in her cabin in isolation.

"I'm not eating very well and have been having fevers," she told CNN in a Skype call Wednesday. "We all are really scared and tense."

Thakkar feared that the virus may be spreading around the crew. At least five have tested positive.