Hong Kong has stepped up surveillance measures at boundary control points as more swine flu cases have been confirmed in Mexico and the United States, a spokesman from Hong Kong's Center for Health Protection (CHP) said on Sunday.

Airlines had been asked to broadcast health advice on all direct flights coming from the affected places and passengers with respiratory symptoms are urged to approach Port Health officers at the Airport for follow-up investigations, the spokesman said.

The spokesman also warned that people traveling to the affected regions should take precautionary measures including avoiding contact with sick people and washing hands frequently with soap and water or apply alcohol-based hand cleanser.

They were also advised to bring along surgical masks for use whenever appropriate, the spokesman said.

The government has upgraded the alert level to "serious" and demanded possible swine flu cases to be reported to authorities, Zhou Yiyue, head of Hong Kong's Food and Health Bureau, told the press after an emergency meeting of local health officials in the afternoon.

The swine flu, which is believed to be a new strain, has killed at least 81 people and sickened thousands across Mexico. Eleven US people were also confirmed to be infected with the virus.

The World Health Organization announced Saturday that the outbreak in Mexico and the United States constituted a "public health emergency of international concern."

In the latest development, 10 New Zealand students who had returned from Mexico were tested positive for the disease.

(Xinhua News Agency April 27, 2009)