A wave of hospitalisations from human metapneumovirus (HMPV) is allegedly sweeping across , with images of packed-out hospitals sparking fears of a second global pandemic.

Users on the Chinese social media app Weibo have reported surges in cases of respiratory illness over the last month, with the YouTube channel Decoding China suggesting that the apparent outbreak is "worse than 2022", when the Omicron variant led to strict lockdown restrictions and thousands of deaths in the country.

One video, which has been reposted on the platform, alleges that patients between 50 and 60 years old have tested positive for the virus before developing pneumonia and requiring hospital treatment between three and five days later.

HMPV is a that becomes more common in different countries at certain times of the year and shares many symptoms with , including congestion, a fever and a persistent cough.

While most cases are mild and non-fatal, HMPV can cause pneumonia, bronchitis and other health complications, especially for elderly and immunocompromised patients.

Weibo users have also posted an influx of concerning images showing hospitals packed out with masked patients, fuelling fears that the virus is spreading across the population and posing a Covid-like threat to the wider world.

While Chinese health officials have remained tight-lipped on the number of confirmed cases and deaths linked to the pathogen, a researcher at the Chinese Centre for Disease Control and Prevention said case numbers were on the downturn on Sunday.

"At present, the rate of positive cases in HMPV detection is fluctuating and the rate of positive cases in northern provinces is declining," Wang Liping said during a press briefing by China's National Health Commission, as reported by AP News.

Gao Xinqiang, deputy director of the commission's Department of Medical Emergency Response, also dispelled claims that the problem was on-par or worse than the height of the Covid-19 crisis.

"There is no obvious shortage of medical resources," he said, adding that rising illnesses across China were being caused by known pathogens rather than any new infectious viruses.

The World Health Organisation (WHO) has also said the upward trend in HMPV cases in China is "within the range expected for this time of year during Northern Hemisphere weather".

The pathogen was first identified in the Netherlands in 2001 and is very similar to flu for most people, spreading through direct contact and via contaminated surfaces.

"While HMPV does mutate and change over time with new strains emerging, it is not a virus that we consider to have pandemic potential," Dr Andrew Catchpole, chief scientific officer at the research organisation hVIVO told the global health partnership GAVI.

"This is because the changes in HMPV are gradual and based on previously circulating strains. Pandemics occur when a totally new virus enters the human population, like for Covid-19," he added.

Data from the UK Health and Security Agency (UKHSA) shows a rise in HMPV cases in the UK, climbing from mid-December onwards. Still, officials have said the numbers are usual for the time of year and don't pose a significant public health risk.