Taiwan has received its final two upgraded early warning aircraft from the United States, a move expected to bolster the island's air defence against rival China, the air force said Sunday.

Analysts say the planes -- which have an all-weather early warning and control system platform with upgraded radar, software, avionics and propellers -- will further reduce warning time if China launched an air attack on the island.

China has repeatedly threatened to invade Taiwan should the island declare formal independence, prompting Taipei to seek more advanced weapons, largely from the United States.

The arrival of the two new E-2Ks brings the number of the advanced aircraft in the Taiwanese fleet to six.

Taiwan acquired four less advanced E-2Ts from the US in 1995 and added two E-2Ks in 2006.

The US then agreed to upgrade the four E-2Ts to E-2Ks as part of a $6.5 billion arms sale that upset Beijing in 2008.

That deal also included advanced interceptor Patriot missiles, Apache attack helicopters and submarine-launched missiles.

The two new planes to be delivered are the last of the four to be upgraded.

The air force declined to provide specifications of the E-2K, which is an improved version of Northrop Grumman's E-2T, but military experts say it is equivalent to the E-2C 2000 now serving the US navy.

Equipped with two eight-blade propellers and a dome on the back which houses antennas for their long-range radars, the planes were transported to the southern port of Kaohsiung Saturday, the air force said.

A picture printed in Taiwan's Liberty Times newspaper showed the two new planes, with their wings folded and fully covered by a white protective plastic sheet, being towed from the harbour to the nearby airport.

The paper said the two aircraft are expected to fly to their home base is southern Pingtung county in a week.

Ties between Taipei and Beijing have improved markedly since Ma Ying-jeou of the China-friendly Kuomintang party came to power in 2008, promising to boost trade links and allow more Chinese tourists to visit the island.

But Beijing still sees Taiwan as part of its territory awaiting reunification, by force if necessary, even though the island has governed itself since 1949 at the end of a civil war.