A pneumonia outbreak that has infected more than 50 people in the Chinese city of Wuhan was caused by a coronavirus, which is the same kind of pathogen involved in the deadly Sars outbreak in 2003, Chinese state media said on Thursday.

The outbreak, which comes ahead of the lunar new year holidays in late January when millions of Chinese will be travelling to see their families, has caused alarm in the region. The virus has prompted widespread concern on Chinese social media and triggered memories of the 2003 outbreak of severe acute respiratory syndrome, or Sars, that infected more than 8,000 people worldwide and killed more than 700, including almost 300 in Hong Kong.

The World Health Organization said, in a statement issued on Thursday, the Chinese authorities believed the disease “does not transmit readily between people”, but noted that it could cause severe illness in some patients.