There has been no report of a suspected or confirmed human case of swine flu in the nation as the epidemic crossed new borders with the first cases confirmed in the Middle East and the Asia-Pacific region.

The number of deaths in Mexico blamed on the virus crossed 150, and the World Health Organization (WHO) raised the alert level to Phase 4 from 3, meaning there is sustained human-to-human virus transmission causing outbreaks

A thermal scanner shows the heat signature of passengers from an international flight arriving at Incheon airport in Seoul Tuesday. The country Tuesday said it had a "probable case" of swine flu - a 51-year-old woman. [Agencies]

President Hu Jintao Tuesday sent a message to his Mexican counterpart Felipe Calderon to express sympathy with families of the vicitms.

State leaders Tuesday called for stepped-up prevention and control measures to cope with the situation.

The directives follow remarks by Dr Hans Troedsson, the WHO Representative in China, who told a press conference Tuesday that there are "flu-like cases under investigation" in the country.

The WHO has been informed that several students were suffering from respiratory symptoms in Shaanxi province; and whether they are linked to swine flu is being investigated, he said.

But tests showed that the students "just caught a cold and had completely recovered by April 22," Liu Shaoming, head of the provincial health administration, told Xinhua.

The Ministry of Health (MOH) Tuesday also said it found no case of confirmed or suspected illness, nor a similar virus in pigs.

Hu and Premier Wen Jiabao have called for beefed-up efforts to prevent human cases.

The State Council also stipulated measures including a "direct reporting system featuring early discovery, early reporting, early diagnosis, early quarantine and early treatment".

A meeting, presided over by Wen, heard reports from central government departments including the MOH on the global situation.

The State Council decided to set up a multi-sector mechanism involving the health and agriculture ministries, the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ), and other related departments.

The meeting did not exclude the possibility of the epidemic spreading to China as "the situation in some countries is developing, more suspected cases have been found and the epidemic-stricken area is expanding".

Among the measures taken so far are:

Special channels will be set up at border check points for people coming from Mexico; and flights and vessels from that country will be disinfected.

Entry-exit inspection and quarantine authorities have been told to be extra vigilant about people and vehicles returning from disease-stricken countries.

The government will issue regular travel notices for citizens going abroad.

The National Tourism Administration has ordered travel agencies to suspend tours to Mexico.

The Ministry of Foreign Affairs alerted Chinese citizens traveling to swine-flu-hit countries to strengthen prevention measures.

Xinhua contributed to the story