Mexico's ambassador says he was denied access to citizens at a hotel
A row is growing between Mexico and China over Beijing's treatment of Mexicans travelling to China following the recent swine flu outbreak.
Mexican officials said their citizens were being unfairly confined. The Mexican ambassador was denied access to a group being held at a Beijing hotel.
China says the steps it has taken are lawful and justified.
Some 400 people have been quarantined in China since the virus was confirmed in a man who arrived from Mexico.
Most are in the Metropark hotel in Hong Kong, where the infected man checked in, but the number also includes his fellow passengers.
No-one else has displayed any symptoms.
Mexico has now confirmed 19 fatalities from the virus, but officials said it appeared that the outbreak could be levelling off.
Mexicans are being held in hotels and other sites across China, including in Shanghai and Hong Kong.
There are reports of international flyers being tested for the virus
Ambassador Jorge Guajardo said many of them had no connection with the Shanghai-Hong Kong flight which carried the infected Mexican man.
"We are objecting to the fact that they are holding Mexicans in isolation for fear that they might have the flu virus, even though they have no signs of having the flu virus," he said.
Mr Guajardo tried to visit 10 Mexicans quarantined in Beijing's Guo Men hotel but was denied access by Chinese officials.
On Saturday Foreign Minister Patricia Espinosa criticised China, along with Peru, Argentina, Cuba and Ecuador, for cutting flights to Mexico.
She also urged Mexicans to avoid travel to China, accusing its government of discrimination for the quarantine measures.
Chinese Ministry of Health spokesman Mao Qunan said extra protection was needed after the virus reached Hong Kong.
"The confirmation of this case clearly raised the risks of A-H1N1 flu entering our country," he said, quoted by state media.
He said the ministry had ordered for all those in "close contact" with the virus to be put under "protective control".