Swine flu will spread further across the world, the World Health Organisation warned, as the number of confirmed cases surged by more than 1,000 and Japan Saturday reported its first domestic infection.
Acting WHO Assistant Director General Keiji Fukuda told reporters that studies indicated a "significant number of people" had been infected, but remained undetected or unconfirmed by laboratory tests.
"Their work also suggests that the virus is transmissible enough that we will expect to see continued community level outbreaks and regional spread," he told a WHO meeting in Geneva on pandemic preparedness.
Following Fukuda's comments, Japan's health minister Saturday confirmed the country's first domestic infection of swine flu, after a high school student who has not travelled abroad tested positive for the virus
The latest WHO data showed 7,520 people in 34 countries were confirmed to have caught the influenza A(H1N1) virus, up 1,000 from Thursday.
According to the figures, most of the deaths had occurred in Mexico, where officials said the death toll rose by two on Friday to 66, with 2,829 having been infected there.
US health officials also upped the number of deaths in the country from three to five, reporting that one person had died in Arizona as well as a young man in Texas.
The US Centers for Disease Control and Prevention (CDC) said the number of confirmed and probable cases had reached 4,714, with only four states -- Alaska, Mississippi, West Virginia and Wyoming -- having been spared so far.
But US officials Friday relaxed a travel advisory for Mexico, three weeks after warning against travel to the country, which has been at the epicentre of the outbreak.
WHO Director General Margaret Chan noted the virus had "quickly demonstrated its capacity to spread easily from one person to another, to spread widely within an affected country and to spread rapidly to additional countries."
"We expect this pattern of international spread to continue," she said.
"This is a time of great uncertainty, and great pressure on governments, ministries of health and WHO," she added.
Fresh updates continued to come in from governments around the world, as Ecuador said it had found its first case.
The 11-year-old victim in the port city of Guayaquil arrived from Miami in the United States only days earlier, said an official, who requested anonymity.
Canadian authorities reported 47 new swine flu cases, bringing the total number of people in the country infected with the virus to 496.
And Japan added to its number of infections.
"Today, the first patient infected with the new type influenza in the country was confirmed," Health and Welfare Minister Yoichi Masuzoe told a news conference.
Earlier this month, Japan confirmed its first A(H1N1) cases -- a school teacher and three students who arrived at Tokyo's Narita International Airport from North America.
Meanwhile, experts warned that the fallout from the swine flu epidemic is hitting the travel industry hard, and international tourism risks sliding heavily if it is upgraded to a pandemic.
"The probability of a full blown pandemic is relatively low, but there might be another outbreak in full force of swine flu in the next winter in the northern hemisphere," an economist at Britain's Oxford Economics firm, John Walker, told AFP.
If that happened the number of passengers could drop "up to 60 percent," he warned.
The WHO's Fukuda said the behaviour of the virus would change depending on "whether it is winter period in one part of the world or another."
The virus had "a very different pattern" from normal, seasonal flu, warned Fukuda: Half of those who had died had been young and otherwise healthy adults.
"Right now we don't know what the future will bring," he added.