China is building its second aircraft carrier, a senior naval officer has told media, the most explicit confirmation yet of a widely expected move that will boost Beijing's maritime power.

China's first aircraft carrier was a 300-metre (1,000-foot) Soviet-era vessel bought from Ukraine and commissioned in September 2012 -- at the time a milestone for the country's growing military might.

Since then "confirmations" from military and government officials of a second domestically built ship have been sporadically reported -- and often deleted shortly afterwards.

The news follows reports last week of another double-digit spending boost for China's military -- the world's largest -- during 2015, as the country pursues a series of territorial disputes with its neighbours.

Senior colonel Liang Fang said China "accumulated a lot of experience" from the first vessel, the Liaoning, and told Internet portal Sohu it had now taken the "next step".

"The reason we imported the first aircraft carrier is so that we could be capable of building our own in the future," she said.

"And now, just like what some media have revealed, that is what we have done -- built the second aircraft carrier," added the officer, a professor at the National Defense University of the People's Liberation Army (PLA).

Liang was responding to a question on senior PLA officers previously confirming the building of the vessel. Her comments were reported Wednesday from an interview on the sidelines of the annual session of the National People's Congress, the communist-controlled legislature.

Beijing has rapidly expanded its military in recent years, rattling its neighbours and attracting the attention of the United States, which is making a foreign policy "pivot" towards Asia.

Last month, authorities in China's eastern Jiangsu province said in an online post that a local firm had won a contract to supply cabling "for China's second aircraft carrier", comments that were picked up by a local newspaper.

The report came just over a year after Wang Min -- the Communist Party secretary of Liaoning province, where China's first aircraft carrier is based -- said the country was already working on a second ship to be completed around 2020.

The "confirmations" of the second vessel appeared to have been removed from the Internet by government censors shortly after they emerged.