The Fujian joins China's fleet as Beijing seeks to project maritime power against the United States and others in the region, with flashpoints including competing territorial claims in the South China Sea and persisting tensions with Taiwan.

The official commissioning, attended by Xi, took place at a naval port in China's southern island province of Hainan on Wednesday, Xinhua reported.

Footage of the proceedings released by state broadcaster CCTV showed Xi and other top officials from the ruling Communist Party (CCP) in attendance at the port.

Analysts say China lags behind the United States, which has 11 aircraft carriers in service, in overall military prowess.

But Beijing has directed billions of dollars into defence in recent years, a trend that has unnerved some governments in East Asia despite China insisting its aims are peaceful.

The navy in particular has seen a massive expansion as leaders seek to grow China's reach in the Pacific and challenge a US-led alliance.

After conducting sea trials in recent months, the Fujian now joins China's other two carriers in active operation, the Liaoning and the Shandong.

The Soviet-built Liaoning is the oldest, commissioned in 2012, while the Shandong entered service in 2019.

Analysts have said that the latest carrier boasts more advanced take-off systems, allowing the Chinese air force to deploy jets carrying larger payloads and more fuel.

- 'Grand and enthusiastic' -

More than 2,000 people from the navy and the carrier's construction units were present at Wednesday's ceremony, standing on the dock in rows, Xinhua reported.

"The atmosphere was grand and enthusiastic," it said.

"After the ceremony, Xi Jinping boarded the Fujian... and learned about the development of the aircraft carrier system combat capabilities and the construction and application of the electromagnetic catapult system," it said.

The Fujian is equipped with an electromagnetic aircraft launch system (EMALS), a more efficient technology than conventional steam-powered methods.

Xinhua said Xi "personally decided" that the Fujian would adopt an EMALS system.

The only other aircraft carrier currently equipped with this technology is the USS Gerald R. Ford.

Xi also went into the carrier's control tower to learn about flight operations, Xinhua said, adding that he "solemnly signed the ship's logbook".

The Fujian had already been in the spotlight several times leading up to its formal commissioning.

Chinese defence officials confirmed in September that the Fujian had sailed through the sensitive Taiwan Strait to carry out "scientific research trials and training missions" in the South China Sea.

The CCP does not rule out using force to seize Taiwan, a democratic, self-ruled island that China claims as part of its territory.

Analysts say the transit was likely intended to send a strong signal to potential adversaries.

Defence ministries in Japan and Taiwan said at the time that they had detected the Fujian's movements, which brought it within approximately 200 kilometres (125 miles) of the disputed Senkaku Islands, known in Chinese as the Diaoyu Islands.

China also released videos in September of aircraft takeoffs and landings aboard the Fujian, including with its fifth-generation J-35 stealth fighter.

State media hailed it as a "new breakthrough" in the development of Chinese carriers and a "major milestone" in the modernisation of the navy.