Beijing  - A Mexican plane arrived in Shanghai Tuesday to collect about 70 Mexican citizens quarantined in mainland China under what Mexican officials called unjustified measures to prevent the spread of swine flu.

The Mexican charter plane was scheduled to fly from Shanghai's Pudong airport to pick up other Mexicans in Beijing, Guangzhou and Hong Kong, one day after the Mexican government accused China of using "unjustified isolation measures" for Mexicans solely on the basis of their nationality.

China's Foreign Affairs Ministry on Tuesday defended its preventative measures against the H1N1 flu strain, which has hit Mexico the hardest, as about 25 Canadian students were placed under a seven-day quarantine in the north-eastern city of Changchun despite passing health checks in Beijing.

The quarantine of the Canadian group was ordered "according to China's relevant regulations and epidemic prevention law" and the local government in Changchun was in regular contact with the Canadian embassy, ministry spokesman Ma Zhaoxu said.

Ma told reporters he could not give the total number of foreigners quarantined in China.

A Chinese charter plane also arrived in Mexico late Monday to fly home about 200 Chinese citizens stranded there since China suspended scheduled flights between Mexico City and Shanghai at the weekend.

China quarantined dozens of Mexican citizens and others who had travelled Thursday on the same flight as a Mexican man infected with swine flu.

His diagnosis represented East Asia's first swine-flu case. A nun, 51, in South Korea has since also been diagnosed.

The 25-year-old Mexican patient, who had recovered by Monday, arrived in Shanghai on an Aeromexico flight with another 175 passengers and 13 crew members.

He flew on to Hong Kong the same day and checked in to the Metropark hotel, where about 300 guests and staff were quarantined for a week after his diagnosis.

Hong Kong leader Donald Tsang on Tuesday offered "thanks and apologies" to the quarantined people but said the isolation measures were necessary.

On Monday, Ma said China's measures were "purely a matter of health and quarantine" and were "not directed at Mexican citizens" after Mexican President Felipe Calderon, in a televised interview late Sunday, had complained that "some countries, out of ignorance and disinformation, insist on taking on repressive, discriminatory measures."(dpa)