China's official death toll and infection numbers from a new coronavirus spiked dramatically on Thursday after authorities changed their counting methods, fuelling concern the epidemic is far worse than being reported.

Two top-ranking politicians overseeing the epicentre of the outbreak were also sacked, adding to questions over China’s handling of the crisis, just hours after President Xi Jinping claimed “positive results” in battling the outbreak.

The World Health Organisation (WHO) also quickly countered Chinese reassurances that the epidemic, which has now officially killed more than 1,350 people in China, would peak in a matter of weeks.

“I think it’s way too early to try to predict the beginning, the middle or the end of this epidemic right now,” said Michael Ryan, head of WHO’s health emergencies programme.

The virus has had massive ramifications globally since emerging from the central Chinese province of Hubei last month, with many countries banning travellers from China in a bid to stop people spreading the disease.

In Hubei, where tens of millions of people are trapped as part of an unprecedented quarantine effort, 242 new deaths were reported on Thursday.

Another 14,840 people were confirmed to be infected with the virus, with the new cases and deaths by far the biggest one-day increases since the crisis began.

The jumps raised the death toll to 1,355 and the total number of nationwide infections of the virus – officially named Coronavirus Disease 2019 (Covid-19) – to nearly 60,000.

Hubei authorities said the huge increases were because they had broadened their definition for cases to include people “clinically diagnosed” via lung imaging.

Up until now, authorities had been documenting cases using a more sophisticated laboratory test.

The commission said it looked into past suspected cases and revised their diagnoses, suggesting that older cases were included in Thursday’s numbers.

On Thursday, the leaders of Hubei and Wuhan were sacked, the highest-profile political scalps of the crisis.

Hubei’s two top health officials had already been sacked this week.

Analysts said Hubei’s new methodology to count infections might be for medical reasons and could be because Xi wants officials to be more transparent, but the immediate impact was to sow more distrust.

“Oddly, this now is a moment of greater transparency,” Sam Crane, a political science professor at Williams College in Massachusetts, said.

“It is not clear if the problem up to now, on this issue, was lack of transparency or simply bad medical practice,” Crane said.

Yun Jiang, a China researcher at Australian National University, said the new methodology may be a “practical measure” because Hubei has a shortage of laboratory testing kits.

“I don’t think the numbers are necessarily manipulated for political purposes but the numbers themselves may not be so trustworthy,” Yun said.

Meanwhile, a team of researchers at Imperial College London believe they are among the first to start animal testing of a vaccine for the virus.

They said their ultimate goal was to have an effective and safe way of halting its spread by the end of the year.

“At the moment we have just put the vaccine that we’ve generated from these bacteria into mice,” Imperial College London researcher Paul McKay said in an interview on Monday.

“We’re hoping that over the next few weeks we’ll be able to determine the response that we can see in those mice, in their blood, their antibody response to the coronavirus.”

Scientists across the world are racing to develop a way to stamp out the new strain of a well-known virus that has been successfully combated in the past.

Imperial College London said it cannot be sure how advanced other teams’ research is at the moment.