The joint naval exercises that China and Russia launched on Sunday morning highlight the warming ties between the militaries and growing cooperation under the China-Russia strategic partnership.

The exercises near Qingdao, Shandong province, will last six days and focus on joint maritime air defense, anti-submarine tactics, maritime search and rescue as well the recovery of hijacked vessels, according to China's Defense Ministry.

"Participating naval forces will train in the prevention of armed conflicts in exclusive economic zones," Russian naval deputy chief of staff Rear Admiral Leonid Sukhanov was quoted by People's Daily as saying.

The two navies will also deploy aircraft and special force units to conduct joint maritime anti-terror drills.

China and Russia have conducted four bilateral and multilateral military exercises since 2005 within the framework of the Shanghai Cooperation Organization, a grouping of China, Russia and four Central Asian states for regional peace.

These exercises are the first dedicated to naval drills.

The number of ships involved was unprecedented, Yin Zhuo, a navy expert, told Chinese media. A total of 16 vessels and two submarines from the Chinese navy were to participate in the drill, including five missile destroyers, five missile frigates, four missile boats, a support vessel and hospital ship, 13 aircraft and five shipboard helicopters.

More than 4,000 Chinese servicemen were to attend the drill, the navy sources said.

The Russian task force, four warships from the Russian navy's Pacific Fleet and three supply ships arrived at the naval base in Qingdao on Saturday.

The Russian warships include the Pacific Fleet's flagship Varyag, a slava-class guided missile cruiser, and the Marshal Shaposhnikov, Admiral Panteleyev and Admiral Vinogradov, three Udaloy-class destroyers.

The main forces from both navies were to participate in the drill, said Zhang Junshe, deputy director of Naval Military Studies Research Institute, calling it a showcase of a high degree of trust between the two sides.

China and Russia, which already conduct frequent military exchanges, want to enhance practical cooperation to counter new challenges and threats in the region, he added.

But AFP said the exercises could cause concerns among China's Asian neighbors since Beijing has experienced more territory disputes recently. The Washington Times said the exercises are an aggressive gesture by the two navies to counter the naval bravado and resolve expressed by the navies of Japan, South Korea and the United States recently.

China's Defense Ministry said the two navies had decided to hold the normal exercises under an agreement reached during a visit by PLA Chief of General Staff Chen Bingduring a visit to Moscow in August last year.

"The exercises China and Russia would conduct are defensive ones, not aiming at any third parties," Zhang said.

"Every military needs drills to test its armed forces through exercises, neither China nor its neighbors are exceptions," he said. "There is no need to speculate about each other's normal military activities."

The Philippines and the US began joint military exercises on April 16 in the South China Sea. The drill is scheduled to end on Friday.