One of the patients Li Wanmei lands at Sanya Fenghuang Airport on April 17, 2016, and is then transferred to the city's No.425 Hospital for treatment. [Photo: Chinanews.com]

China has hit back at U.S. criticism over a Chinese military aircraft that landed on a reef in the South China Sea.

During a Pentagon briefing, spokesman Jeff Davis said it was unclear why China had used a military aircraft, as opposed to a civilian one, to evacuate workers who needed urgent hospital treatment.

China's Foreign Ministry spokesperson, Hua Chunying, said dispatching a military aircraft for humanitarian purposes was an international norm.

"China has explained the case that Chinese military aircraft carried three severely wounded patients from Yongshu Reef to Sanya City of Hainan Province. It is a generally known common practice of nations that military aircraft participate in rescue work, providing humanitarian aid and helping civilians with evacuation; and we can see that Chinese military aircraft always arrive at accident sites for rescue work."

Hua stressed that, on Chinese territory, Chinese military aircraft and military personnel will be deployed at anytime or in any place they were needed.

She went on to urge the United States to take real action to safeguard peace and stability in the South China Sea.

In a statement on its website, China's Defense Ministry said rescuing people in danger is a fine tradition of the Chinese military.

The statement said the construction and defense facility deployment on the islands and reefs involved, are within China's sovereignty, and said that the United States should stop making accusations.