Health authorities in east China's Shandong Province put 23 people under home or hospital quarantine on Thursday morning to check for symptoms of A/H1N1 influenza, the provincial health department said.

The 23 had been in close contact in a Beijing-Jinan train with a male resident of Shandong who health officials said Wednesday had tested positive for the disease.

The provincial health authorities are seeking 20 other passengers who were in the same car of train D41, from Beijing to the provincial capital of Jinan, on Monday.

After the man was diagnosed, Shandong Province declared China's first swine-flu health emergency at about 6:00 PM on Wednesday.

Wang Suilian, vice governor of the eastern province, said Shandong declared the second-level health emergency, which will involve many departments coordinating to contain the disease and keep the public informed.

Shandong's flu case, the second known case on the Chinese mainland, involved a 19-year-old student surnamed Lv who arrived in Beijing from Canada on May 8 and traveled to Jinan three days later.

Lv was hospitalized Monday. He was recovering with a normal body temperature on Wednesday, when he was taken off intravenous feeding.

"We only prescribed some anti-influenza medicine like Tamiflu for Lu," Dr. Ma Jiren, who is also deputy director of Jinan's Health Bureau, said on Thursday.

Lv is in an isolation ward in the Jinan Hospital of Infectious Diseases.

Zong Lin, chief of the disease control and prevention section of the Shandong Provincial Health Bureau, said health officials were sending text messages and running notices on TV to find the remaining passengers.

A health official surnamed Zhang said that the second-degree emergency declaration was the highest-level response available to provincial governments. A first-degree emergency declaration would be up to the central government.

Beijing launched a second-degree emergency response against bird flu in January after a 19-year-old woman died of the disease in the capital. The city's poultry markets were closed and disinfected, and disease control staff went door-to-door in suspected infection areas to check flu patients.

"A second-degree emergency can be declared when an A-class infectious disease is confirmed. The A/H1N1 influenza is currently classified as B-class infectious disease in China.

"However, the health department proposed the emergency be declared immediately, because the scientific community is still unclear about how the virus spreads and there is a high risk of a mass outbreak," he said.

The mainland's first A/H1N1 flu patient, who has been at the Chengdu Infectious Diseases Hospital in southwest Sichuan Province for four days, was making a rapid recovery.

All 147 passengers who had been exposed to that patient on Northwest Airlines flight NW029 from Tokyo to Beijing, had been contacted by the Beijing Health Department, said the department on Wednesday.