As requested by the Ministry of Health, hospitals have to closely monitor patients from or who have visited Wuhan in central China where a strain of pneumonia has infected 59 people, with seven in critical condition as of Tuesday, according to official data.

The ministry demanded health departments across the country tighten health checks at border gates, and utilize remote body temperature meters for quarantine and test purposes.

China's Ministry of Health is investigating the source of the outbreak, which it seeks to contain as soon as possible.

The viral illness was first reported in Wuhan last week, though Chinese health officials have ruled out a resurgence of the highly contagious SARS virus, which killed hundreds more than a decade ago, after fears spread online it had made a comeback.

Avian flu and Middle East Respiratory Syndrome (MERS) have also been ruled out, AFP reported.

In Hong Kong, authorities say 21 people have been hospitalized after returning from Wuhan in recent days and displaying flu-like illnesses but none were confirmed to have contracted the mystery new strain.

"The reported link to a wholesale fish and live animal market could indicate exposure to animals," the World Health Organization stated Sunday.

"Pneumonia is common in winter," it added, saying the concentration of cases should be handled "prudently."