The airfield will provide more routes for flights over the South China Sea, according to a government media release.
Insiders, who declined to be named, said the test flights were different from the one reported on Saturday. That flight aimed to test communication between the planes and the airfield, while Wednesday's were "real test flights".
Foreign Ministry spokeswoman Hua Chunying confirmed on Saturday that China had finished building an airfield on Yongshu Jiao in China's Nansha Islands. It is the most southerly airfield in the country.
She said Saturday's test flight was intended to check whether the runway met civilian aviation standards.
Xinhua News Agency reported that two civilian aircraft departed from Haikou in Hainan province on Wednesday morning and landed on Yongshu Jiao after flights of nearly two hours. They returned to Haikou in the afternoon.
The official media release by Xinhua said, "The test flights proved that the airfield has the capacity to ensure safe operation of large civilian aircraft."
This will help with the transportation of goods and personnel as well as with healthcare on the islands, it said, adding that the airfield will also serve as an alternate one for flights in the region.
Pan Wei, chief engineer at China Rescue and Salvage under the Ministry of Transport, said the airfield will significantly cut travel time between the Nansha Islands and the Chinese mainland.
Pan said the airfield will help to ensure flight and navigational safety for airplanes and ships in the area and greatly improve the ability of marine salvagers.
As a responsible country, China will continue to promote the building of emergency response and rescue facilities, Pan said.
It will shoulder the international obligations of search and rescue operations, marine environmental protection, disaster prevention, and navigational safety in the South China Sea.
Nearly 40 percent of global trade is carried through the South China Sea, which sees the passage of at least 40,000 ships annually.
Vietnam and the Philippines have protested over the new airfield's completion. But Hua said on Saturday the test flight that day was completed "completely within China's sovereignty".
Xinhua contributed to this story.
