China lifted a swine flu quarantine for a group of Canadian students two days early, after Ottawa and the World Health Organization asked Beijing to explain such measures, but said it would continue its strident checks on travelers from affected regions. Other Asian countries remained on guard. The group of 25 students and a professor from a Canadian university had been under "observation" at a hotel in the northeastern Chinese city of Changchun since the weekend but were released Wednesday instead of Friday because they were healthy, an official said. China has been accused in the past of not acting quickly enough to combat the spread of diseases, especially the 2003 global outbreak of SARS. Chastened by that experience, and subsequent threats from avian flu, the government this time has acted quickly and decisively to block an outbreak, but some of its measures have been criticized as unnecessary.