The Chinese military aircraft has for the first time publicly landed at a new airport on an island built by China in the disputed South China Sea, raising the prospect that the country could base fighter jets there.
The United States has criticised China's construction of artificial islands in the South China Sea and is worried that it plans to use them for military purposes, even though China says it has no hostile intent.
The runway on the Fiery Cross Reef is 3,000 metres (10,000ft) long and is one of the three which China has been building for more than a year.
Civilian flights began test runs there earlier in January.
A military aircraft on patrol over the South China Sea on Sunday received an emergency call to land at Fiery Cross Reef to evacuate three seriously ill workers.
They were taken in the transport aircraft back to Hainan island for treatment.
It was the first time China's military had publicly admitted landing an aircraft on Fiery Cross Reef.
It cited a military expert as saying that the flight showed the airfield was up to military standards and could see fighter jets based there in the event of war.
The runways would be long enough to handle long-range bombers and transport aircraft as well as China's best jet fighters, giving it a presence deep in the maritime heart of south-east Asia that it has lacked until now.
More than five trillion dollars of world trade is shipped through the South China sea every year.
