The World Health Organization said Thursday that the number of laboratory confirmed cases of H1N1 influenza A, the so-called "swine flu," has jumped to 257 people around the globe.
The figure represents a significant climb from the 148 confirmed cases the WHO was aware of on Wednesday.
Dr. Keiji Fukuda, a spokesperson for the WHO, said Mexico saw the largest jump, with cases up from 26 to 97.
"The jump in numbers being reported by Mexico probably represents a lot of the work which is being done right now to go through the backlog of specimens which have been collected from people with the different symptoms," Fukuda said Thursday from Geneva.
"They're going through several thousands of specimens right now trying to identify those which may be positive for the H1N1 virus."
The WHO raised its alert level to Phase 5 Wednesday, meaning the probability of a pandemic is "high to certain," as the virus spreads around the planet.
"We do not have any evidence to suggest that we should move to Phase 6 today or (that) any such move is imminent right now," Fukuda said Thursday.
Phase 6 would indicate that a global pandemic is under way.
The H1N1 flu is blamed for nearly 170 deaths in Mexico, although many have yet to be officially confirmed. Nearly 3,000 are believed to have contracted the virus in Mexico.
To stop the spread of the virus, Mexico has ordered a suspension of nonessential federal government and private business activity from May 1-5.
In a televised address, Mexican President Felipe Calderon urged Mexicans to literally stay in their houses during the temporary shutdown.
"There is no safer place to protect yourself against catching swine flu, than in your house," Calderon said.
Calderon rejected criticisms that his government responded slowly to the outbreak, which was first reported in Mexico, saying that officials sprung to action "immediately."
CTV's Tom Walters, reporting from Mexico City, said the mood there is very sombre as people are concerned about catching the disease.
"Compounding that is the awareness of what this is doing economically to their country at a time when every country is in some economic stress to begin with," Walters said.
Meanwhile, in Luxembourg, EU health ministers were holding emergency talks Thursday to co-ordinate how to stop the spread of the H1N1 virus.
"We are expecting the situation to develop further, but there is no cause for panic," EU spokeswoman Nina Papadoulaki said. "We are all ready to manage the situation ... we are doing everything we can."
EU ministers are expected to discuss the possibility of issuing a Europe-wide travel advisory for Mexico.
The talks come as Switzerland confirmed its first H1N1 flu case Thursday -- a 19-year-old student who was mistakenly released from hospital and then quickly brought back.
In Europe, Britain, Spain, Austria, Germany, The Netherlands and Switzerland have already confirmed H1N1 cases.
Fifteen more cases of H1N1 flu were reported in Canada Thursday, raising the total to 34.
South of the border, 116 cases have been identified in the U.S. but most appear to be mild forms of the disease.
However, a Mexican toddler died Monday night in Houston, the first fatality in the U.S.
The H1N1 flu virus is normally contracted through contact with pigs.
However, this strain is spread through human-to-human contact.
Symptoms include fever, muscle and joint pain, cough, sore throat, eye pain, shortness of breath and extreme fatigue.
With files from The Associated Press
