HONG KONG: A Mexican jet flew scores of its nationals home from cities across China early Wednesday after they were quarantined under strict swine flu measures which drew protests and triggered a diplomatic row.

The trip, taking in Shanghai, Beijing, Guangzhou in the south, and Hong Kong, came after China at the weekend suspended flights to and from Mexico, the epicentre of the outbreak, leaving tourists at both ends stranded.

Amid frosty ties between China and Mexico over Beijing's handling of Mexican nationals, a chartered AeroMexico flight landed first in Shanghai where it was due to collect around 70 Mexicans, including 43 quarantined there.

At a Shanghai hotel, armed police supervised masked medical staff in protective clothing transferring Mexicans into about 30 ambulances taking them to the airport, said Eastday.com, a website run by the city government.

In Beijing, eight quarantined Mexicans were taken to the airport and left the capital, according to the official Xinhua news agency.

The AeroMexico flight picked up 12 people in Hong Kong and left at 3:41 am (1941 GMT), according to a spokeswoman for the Hong Kong government.

But Hong Kong's only confirmed case of swine flu, which precipitated China's suspension of flights, would not be allowed to join the other Mexicans going home, the territory's under-secretary for food and health Gabriel Leung said.

The jet was also due to fly home Mexicans who had not been quarantined but were stuck in China after Beijing suspended flights to Mexico, with 152 people expected to go back in total, a Mexican diplomatic source in Beijing told AFP.

Mexican diplomats have complained that 70 of their nationals were put in isolation in mainland China despite showing no signs of the (A)H1N1 virus.

Some of the quarantined Mexicans had travelled to China on board the same flight that carried an infected Mexican man -- Asia's first confirmed case of swine flu -- who is now in a Hong Kong hospital.

The illness, which appears to have originated in Mexico, has spread across more than 20 countries and killed 30 in all, according to the World Health Organisation.

Defending its handling of the affair, China denied targeting Mexicans with its flu measures, saying they were "not directed at Mexican citizens and are not discriminatory."

And in a statement on the central government's website Tuesday, China said it would continue to impose strict medical examinations on travellers from flu-affected countries and regions.

Waiting at Mexico's embassy to secure a seat on the flight, Mexican Pedro Diaz described how some hotels had refused to take him in after seeing his passport. The 28-year-old had been stuck in Beijing by the flight suspensions.

China, meanwhile, also sent a plane to Mexico to fetch dozens of its citizens stranded by the flu crisis there, China Southern Airlines said in a statement, after the two countries agreed on a repatriation deal.

That plane was forced to land in Los Angeles because of bad weather in the Mexican city of Tijuana, on the border with the United States, the official Xinhua news agency reported early Wednesday.

The chartered aircraft picked up 79 Chinese nationals in Mexico City and was on its way to collect 20 more in Tijuana, Xinhua said.

Amid further discontent with how China was dealing with international visitors from countries with confirmed flu cases, Canada has asked Beijing to explain the quarantine at the weekend of 22 students.

One of the students, Martin Leroy Deslauriers, told AFP by phone from the hotel that none of the students had any symptoms and they believed they were singled out by authorities in the city of Changchun for being Canadian.

Canada has one of the highest numbers of cases of the virus.

"I am sure they have their reasons but I think its mostly symbolic because we are Canadian and some people had the flu in Canada," said Deslauriers, 26, from Montreal.

None of the hotel staff wore masks and teachers from the local university were allowed to come and go freely to teach classes at the hotel, he said.

Separately, at least four US citizens are now or have been quarantined in China, a US embassy official told AFP.