The incident erupted on Tuesday when a Russian A-50 early warning and control plane violated airspace over the Dokdo islands, Seoul said. The islands are also claimed by Tokyo.

South Korea scrambled fighter jets, which fired nearly 400 warning shots at the alleged intruder.

The Chinese and Russian warplanes "strictly abided by the relevant regulations of international law and did not enter the airspace of other countries", defence ministry spokesman Wu Qian told a news conference in Beijing.

He did not mention an A-50, the Russian plane Seoul said violated its airspace.

Moscow has also denied any airspace violations by the long-range bombers -- two Russian Tu-95s and two Chinese H-6Ks -- which Beijing said flew over the East China Sea and the Sea of Japan in the first joint patrol by the two nations in the Asia-Pacific region.

The patrol aimed to deepen the comprehensive strategic cooperative partnership between China and Russia, enhance joint operation capabilities of their armed forces, and "jointly safeguard global strategic stability", Wu said.

"This operation is within the annual cooperation plan between the Chinese and Russian armed forces, and does not target third parties."