Two people were in critical condition in a Hong Kong hospital suffering from swine flu

Two people were in critical condition in a Hong Kong hospital suffering from swine flu, according to health officials, a year and a half after an outbreak killed more than 80 people in the city. Hong Kong, a city of seven million, has some of the world's most densely populated neighbourhoods, prompting a panicked response from many residents over news of a disease outbreak. Some wear surgical masks to avoid infection.

But there are worries the disease could spread over the next few weeks in the run up to Lunar New Year, when hundreds of millions of Chinese travel across the country to celebrate with families.

Swine flu has killed more than 18,400 people and affected practically all parts of the world since it was uncovered in Mexico and the United States in April 2009, according to the World Health Organization. Hong Kong was the site of the world's first major outbreak of bird flu among humans in 1997, when six people died of a mutation of the virus, which is normally confined to poultry.