Severe Acute Respiratory Syndrome, or SARS, first reported in Asia in February 2003 and spreads to 29 countries before being contained in May 2004.
The World Health Organisation says Sars killed 774 people and sickened 8,098 others.
First human infections with H5-N1 virus, or 'bird flu', reported in Hong Kong in 1997. Six out of 18 cases prove fatal.
By 2009, 257 deaths from bird flu are recorded worldwide, with Indonesia the worst hit. Seven people in China and Vietnam die.
Ebola Reston virus found in pigs and six humans in the Philippines in 2009 in what is believed to be the virus' first transmission from pigs to humans.
"The scare is very genuine and it could spread further and become a pandemic,' Dr John Simon, a consultant in infectious diseases and tropical medicine in Hong Kong, told Al Jazeera.
"We don't know yet ... how many people it is going to kill," he said.
"It is an H1N1 virus and that is easy to treat with anti-viral drugs - I am not saying it is going to be easily containable, but it should be quite responsive to treatment.
"The H5N1 ['bird' flu] is also still there ... as a background candidate for a new pandemic."
The World Health Organisation (WHO) warning will alarm many of Asia's governments as previous outbreaks have killed many people and reduced tourism in the region.
The WHO on Saturday declared the outbreak of the new strain a "public health emergency".
"This virus has clearly a pandemic potential," Margaret Chan, director-general of the WHO, said.
Ten students from New Zealand who travelled recently to Mexico have tested positive for influenza and are "likely" to have contracted swine flu, Tony Ryall, the country's health minister, said on Sunday.
Felipe Calderon, the Mexican president, issued an emergency decree on Saturday giving the government special powers in attempt to control the outbreak.
The decree gives the government power to isolate sick people, enter homes or workplaces and regulate air, sea and land transportation to try to stop further infection.
Franc Contreras, Al Jazeera's correspondent in the capital Mexico City, said the authorities had advised people not to go outside unless necessary and that many residents had bought surgical masks in an attempt to stave-off the disease.