China's first aircraft carrier entered service on Tuesday, the defence ministry in Beijing said, as the country expands its blue-water fleet at a time of increasing maritime tensions in the region.

The ministry named the 300-metre (990-foot) vessel, a former Soviet ship bought from Ukraine, the Liaoning after the northeastern province that is home to China's main naval port city of Dalian, where it was refitted.

The commissioning makes China the last permanent member of the United Nations Security Council to have an aircraft carrier, and comes as Beijing's economic and political significance grows.

Numerous sea trials of the aircraft carrier -- which was previously only known as "Number 16" -- since August 2011 were met with concern from regional powers including Japan and the United States, which called on Beijing to explain why it needed such a ship.

"Having the aircraft carrier enter the ranks will be of important significance in raising the overall fighting capacity of our nation's navy to a modern level," the defence ministry said.

It "will be effective in defending the interests of state sovereignty, security and development and advancing world peace and common development."

The ministry also said the vessel will increase China's capacity to defend itself and "cooperate on the high seas in dealing with non-traditional security threats".

There had been swirling speculation on what the vessel was to be called, with retired Major General Luo Yuan suggesting naming it Diaoyu, after islands in the East China Sea claimed by China, which are also claimed by Japan and called Senkaku by Tokyo.

Beijing on Sunday postponed a ceremony marking the 40th anniversary of the establishment of diplomatic ties with Tokyo.

Tensions have also risen this year with Vietnam and the Philippines over disputed islands in the South China Sea.

Beijing confirmed last year it was revamping the former Soviet ship -- originally called the Varyag -- and has repeatedly insisted the carrier poses no threat to its neighbours.

It says the ship will mainly be used for training and development purposes, but military commentators say China is developing strike aircraft and support vessels which would help the ship become fully operational.

Pictures have been published in the Chinese press showing domestically built planes on the carrier's deck.

Leading generals have also said that developing strike aircraft for China's navy is a top priority for military bosses.

"To achieve China's great cause of national rejuvenation, China should not only be a land power but also a sea power," said Yang Yi, a rear admiral in the Chinese navy in a commentary in the state-run China Daily newspaper Tuesday.

"While China is facing the threat of various external security challenges, the development of its aircraft carrier has been the common aspiration and will of the entire nation."

Domestic press said on Sunday that the vessel had been handed over to the navy of the People's Liberation Army by its refitters.