China ramped up efforts to contain swine flu and awaited confirmation Wednesday of a second suspected case on the mainland, as the number of infections worldwide soared past the 5,000 mark.
State news agency Xinhua said a man was under treatment in eastern China's Shandong province where he had arrived by train after flying to Beijing from Canada.
China has already isolated 349 people, including foreigners, who travelled with the mainland's first swine flu case.
However this second case raises the prospect of hundreds more having to be traced and quarantined -- a hugely complex task in the world's most populous nation.
The World Health Organisation (WHO) said Tuesday more than 5,250 cases had been reported in 30 nations, around half of them, including three deaths, in the United States.
More than 2,000 other cases are in Mexico, the origin of the outbreak where the WHO has confirmed 56 fatalities and national authorities reported a further two.
Cuba, Finland and Thailand reported their first cases Tuesday while Canada said the virus, officially known as influenza A(H1N1), had reached the Yukon Territory in its far north, which traverses the Arctic Circle.
China has ordered heightened nationwide flu vigilance and urged anyone who travelled on the train or plane with the second suspected case to report in.
The 19-year-old student boarded the train to Jinan despite having a strong fever, the health ministry said, and alerted local authorities who picked him up on arrival.
Earlier, an official with the Beijing municipal health authority told AFP 78 foreigners were among those quarantined at a hotel in the capital for seven days.
"We are faced with even more serious challenges now," Vice Health Minister Ma Xiaowei was quoted as saying by Xinhua news agency.
Mexico began pumping one billion dollars of emergency cash into its economy as officials there revealed tourist cancellations had forced 25 hotels in and around the resort of Cancun to close.
Health Minister Jose Angel Cordova said the epidemic in Mexico appeared to be waning. "Tourist destinations are safe in Mexico, people can return calmly, we are carrying out intensive checks," he added.
However, a report by a WHO pandemic assessment team estimates 23,000 people were infected in Mexico, while US officials said their numbers were also just the tip of the iceberg.
Most of the cases have been treatable with antiviral drugs, and Swiss drugs giant Roche said it was donating 5.65 million treatment courses of Tamiflu, although a WHO expert said the virus was developing resistance.
Meanwhile, four countries, Ecuador, Honduras, Kazakhstan and the United Arab Emirates, lifted restrictions on Mexican pork imports applied after the outbreak of A(H1N1), Mexico's economy ministry said Tuesday.
China and Russia are among others to have suspended pork imports from some swine flu-affected nations, although the WHO and others say there is no evidence the meat is a source of infection.
The Japanese women's football team cancelled three friendly matches in the United States and Canada because of swine flu fears.
On a brighter note, a 25-year-old Spanish woman recovering from flu, it was not immediately clear what strain she contracted, emerged from her sick bed to claim a record 126 million euros (172 million dollars) in a lottery.