Under criticism at home over the handling of the crisis, China's Communist Party sacked two top-ranking officials in Hubei province, the epicentre of the outbreak.

"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.

In Hubei and its capital Wuhan, 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 new cases and deaths by far the biggest one-day increases since the crisis began.

The additions raised the death toll to 1,355 and the total number of infections nationwide to nearly 60,000.

Hubei authorities said the increases were because they had broadened their definition for infection to include people "clinically diagnosed" via lung imaging.

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

Health officials said they looked into past suspected cases and revised their diagnoses, suggesting older cases were also included in Thursday's numbers.

Authorities in Hubei have been accused of concealing the gravity of the outbreak.

Criticism intensified after the death of a doctor who had tried to raise the alarm about the outbreak in December, but was silenced by authorities.

Transparency

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

Hubei's two top health officials were fired earlier this week.

"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 told AFP.

Global havoc

In Vietnam, authorities announced they were locking down the commune of Son Loi, a farming region about 40 kilometres (25 miles) from Hanoi, for 20 days.

Checkpoints were set up around the commune, according to AFP reporters in a district on the outskirts of Son Loi. Health officials wearing protective suits sprayed disinfectant on vehicles.

United Airlines extended its China flight cancellations into late April.

The outbreak has wreaked havoc with global events, with the World Mobile Congress in Spain cancelled and the Formula One Grand Prix in Shanghai postponed. —AFP