The latest delivery was part of a contract signed in June 1999 under which the central government agreed to buy 72 fighters and take on licensed production of 250 more.

The design bureau official also declined to comment on a Washington Times report that the aircraft would be equipped with AS-17x missiles as part of the deal.

A Hong Kong-based military expert said procurement of the fighters was essential to the PLA's modernisation programme.

Ma Ding-shing, a veteran PLA observer, said the mainland's air force, which only had about 300 modern jets, would surpass the strength of Taiwan's capabilities by 2010 or 2015.

The island now possesses 430 advanced fighters, including F-16s, Mirages and a self-developed model called Ching-kuo.

'The older Su-27 is seen as an aircraft only good for defence because it is not equipped with powerful reconnaissance radar,' said Mr Ma.

'The Su-30 plane, however, is excellent in its air-to-ground and air-to-air reconnaissance performance.'

Mr Ma said the Su-30 was able to form a battle group with four Su-27 fighters, which would enhance the PLA air force's attack capacity.

He thought the air force's latest purchase evened the balance of power with Taiwan.

Over the past decade, the mainland has been involved in 34 major weapons deals and the purchase of one production licence, which allows for the assembly of 50 Su-27 aircraft in China.

The weapons purchased by the mainland have included eight Ka-27 helicopters, four Kilo-class submarines and two Sovremenny-class destroyers.