Hong Kong authorities have activated a newly created ‘serious response’ level as fears spread about a mysterious infectious disease that may have been brought back by visitors to a mainland Chinese city.

The government launched a new response plan Saturday for infectious diseases of unknown cause.

It had earlier stepped up temperature checks at border crossings.

At least 44 people have been infected in the city of Wuhan, and five possible cases have been reported in Hong Kong.

The outbreak has revived memories of the 2002-2003 SARS epidemic, which killed more than 700 people in mainland China, Hong Kong and elsewhere.