A satellite image of China's first aircraft carrier has been captured while the vessel was undergoing sea trials in the Yellow Sea, a US company said on its website Thursday.

The 300-meter (990-foot) ship, a refitted former Soviet carrier, was photographed on December 8, said Colorado-based DigitalGlobe Inc., and an analyst from the company spotted it when reviewing images five days later.

The Beijing government said earlier this month that the carrier had started its second sea trial after undergoing refurbishment and testing.

The ship underwent five days of trials in August that sparked international concern about China's widening naval reach amid growing regional tensions over maritime disputes and a US campaign to assert itself as a Pacific power.

The South China Sea, which is believed to be rich in oil and gas and is claimed by several countries, has dominated such disputes involving China, leading to run-ins with rival claimants including Vietnam and the Philippines.

Chinese President Hu Jintao on December 7 urged the navy to "accelerate its transformation and modernization" and "make extended preparations for military combat" to safeguard national security.

Beijing only confirmed this year that it was revamping the Soviet ship, the Varyag, and has repeatedly insisted that the carrier poses no threat to its neighbors and will be used mainly for training and research purposes.

But the August sea trials were met with concern from regional powers including Japan and the United States, which called on Beijing to explain why it needs an aircraft carrier.

China only provided the first official acknowledgment of the carrier in June when Chen Bingde, the nation's top military official, gave an interview to a Hong Kong newspaper.