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.