Tests carried out on children in northern China have shown they are not infected with potentially fatal swine flu, the health ministry said.
The ministry issued the statement after the World Health Organization's representative in China said Tuesday he believed a school in Shaanxi province had been shut as a precautionary measure after several children fell ill.
"The students had symptoms of respiratory infections," Hans Troedsson told reporters.
But the health ministry said in a statement posted on its website late Tuesday that 63 students and teachers at a junior high school in Shaanxi had merely contracted regular, seasonal flu and that none was hospitalised.
The ministry said tests on six of the patients showed they were suffering from influenza B, a strain commonly seen in humans -- not the swine flu identified as A/H1N1, believed to have killed more than 150 people in Mexico.
A total of 60 students and three teachers at the Qianwei township junior high school in Lantian county had fallen ill between April 10 and 16, according to the ministry.
"They just caught a cold and they had completely recovered as of April 22," the head of the provincial health department, Liu Shaoming, told the state Xinhua news agency.
The school was closed for a week and reopened on April 22, the health ministry said.
The was no mention of whether or not any of the children had visited Mexico or any other affected areas. A WHO spokesman said Tuesday he did not believe any of them had visited anywhere with a confirmed outbreak.
The potentially fatal virus has so far spread to the United States, Canada, Costa Rica, Europe, Israel and New Zealand. Suspected cases have been detected in several other countries.
China -- heavily criticised for initially covering up the SARS epidemic in 2003 -- went on full alert Tuesday to prevent an outbreak of swine flu, stepping up surveillance and monitoring mechanisms nationwide.
The WHO's Troedsson said there were so far "no confirmed and no probable cases in China."
The government pledged to make fighting the virus its "central task" and also promised openness in reporting any eventual confirmed cases.