The world could be "venturing into the unknown" after the outbreak of a new mystery illness in China, a health expert has warned.

A surge in cases of pneumonia in the Asian country has led to demands for answers from the World Health Organisation (WHO) and country across the globe.

Just three years after Covid-19 was able to spread rapidly due to China's secrecy over the virus, health officials are eager to avoid a repeat scenario.

Asian neighbours of China have already started to close their borders and the WHO has demanded a return of face masks in Beijing.

Amid the uncertainty, Dr Joseph Ambani, an expert in infectious diseases, has described the lack of knowledge about the mystery illness as "worrying" for countries in Europe.

"[Understanding] whether it's a novel strain or a mutation of an existing virus is critical," he told the Daily Express.

"This knowledge shapes our predictions about its spread and virulence.

"If it's a novel virus, we're venturing into the unknown, with potential for both higher virulence and a lack of immunity in the population."

Face masks were advised by the World Health Organisation

While an outbreak in Europe is yet to take place, Denmark has been hit by an increase in pneumonia cases.

As many as 541 cases of mycoplasma pneumonia were recorded in week ending November 26.

Hanne-Dorthe Emborg, an SSI researcher in the country said: "There is widespread infection throughout the country."

She added: "The number of new cases has increased significantly [in recent weeks], and we are now seeing significantly more cases than usual."

Ambani urged European nations to prepare now in case of a sudden outbreak.

He said: "Europe must not only ramp up surveillance but also ensure its healthcare infrastructure – from ICUs to primary care – is equipped to handle a potential surge in cases.

"This preparedness extends to stockpiling essential medical supplies and training healthcare professionals in epidemic management."