The EU has warned against non-essential travel to Mexico and the United States as fears of a pandemic grow. Spain has become the first European country to confirm a case of swine virus.
Churches stood empty Sunday in Mexico City after services were cancelled
European Union Health Commissioner Andorra Vassiliou warned people to avoid travelling to areas where a health threat is posed by swine flu.
"I would try to avoid non-essential travel to the areas which are reported to be in the center of the cluster," she said.
European Union foreign ministers held talks on Monday in Luxembourg on the outbreak of swine flu, and EU health ministers are also due to hold an emergency meeting on the topic on Thursday.
The EU's Czech presidency said it was of "paramount importance to coordinate (the) EU's response to the outbreak".
Spain confirms first case
A police officer guards the entrance to the Metropolitan Cathedral in Mexico City
The Spanish health ministry has confirmed its first case of swine flu - a young man who was diagnosed after returning from a trip to Mexico. The man is being kept isolation but is reportedly in good condition.
Spanish authorites said that 17 other people were suspected of having the disease.
In the northeast region of Catalonia, three people were in quarantine in addition to four others in Bilbao and Teruel in the north, in Almansa in the southeast and Valencia in the east, health officials said.
All had recently returned from Mexico.
The Spanish government has asked AENA, the company that manages Spanish airports, to hand over lists of people on flights that brought the seven back, officials said.
Spain has advised citizens who have recently returned from Mexico to monitor their health.
Germany on alert
German authorities have also advised cabin crews arriving at Frankfurt's international airport from Mexico or other swine-flu-affected areas to report any sick passengers.
Pamphlets on precautions and symptoms of the virus will also be distributed to travellers at airports in the country.
Germany says recent highly infectious human diseases have arrived through Frankfurt airport
The health ministry says there is no immediate threat to Germany's population.
Germany's largest tour operator TUI has suspended all trips to Mexico City, but says trips to other parts of Mexico will continue.
Fears of a pandemic
In Mexico, where the flu has claimed more than 100 lives, people hid indoors to avoid the deadly virus. Mexican officials say the number of suspected swine flu cases has risen to 1,614.
The United States confirmed at least 20 new cases of the swine flu on Sunday and US President Barack Obama has ordered a "very active, aggressive, and coordinated response," according to White House officials.
Canada has also confirmed human cases of swine flu. Nova Scotia's chief public health officer, Dr. Robert Strang, said the east coast Canadian province had confirmed four "very mild" cases of the flu in students ranging in age from 12 to 17 or 18. All are recovering, he said.
Nations from New Zealand to France have also reported suspected cases and some warned citizens against travel to North America while others planned quarantines, tightened rules on pork imports and tested airline passengers for fevers.
A new strain
The WHO has urged governments to be vigilant
The new flu strain is a mixture of four different swine, bird and human viruses. It poses the biggest risk of a large-scale pandemic since avian flu surfaced in 1997, killing several hundred people.
New flu strains can spread quickly because no one has natural immunity to them and a vaccine takes months to develop.
World Health Organization Director-General Dr. Margaret Chan urged greater worldwide surveillance for any unusual outbreaks of influenza-like illnesses.
The WHO has declared the flu a "public health emergency of international concern" that could become a pandemic.
A pandemic would deal a major blow to a world economy already suffering its worst recession in decades, and experts say it could cost trillions of dollars.