A delegation of Vietnamese military and government officials was treated to a tour aboard the sprawling USS George Washington nuclear carrier this weekend off the country's southern coast, once home to the US-backed capital of South Vietnam during the brutal Vietnam War.

It's the second such visit to the US Navy's hulking carrier in as many years and a symbol of the former foes' warming military ties. But Saturday's visit also came amid heated tensions between China and its Asian neighbours. Hanoi's relations with Beijing hit a low point this summer following weeks of squabbling over disputed territory in the South China Sea - where the US carrier cruised under blue skies about 140 miles (225 kilometers) off the coast.

On Wednesday, China launched its first carrier on a test run. The refurbished former Soviet vessel, once named the Varyag, was rebuilt over about a decade from a stripped-down hull. Beijing has said it plans to use the carrier for research and training, which could lead to the buildup of more like it in its own shipyards.

Washington has urged secretive China to provide more transparency about its military growth, but Capt. David A. Lausman, commanding officer of the USS George Washington, said while at helm of the massive beast that a carrier alone is nothing without experience and a highly skilled crew.

"We operate normally 100 takeoffs and landings a day," he said from his lofty view of the ship overlooking the 1,092-foot (333-metre) flight deck and flanked by the USS John S. McCain warship. "We can do that every day, day in and day out, because of their training. That's what makes a carrier, not just going to sea in a floating big ship."

The US operates 11 aircraft carrier battle groups and spends around $550 billion a year on defense, not counting the wars in Iraq and Afghanistan. China's defense budget has steadily increased to become the world's second highest after the US, spending $91.5 billion last year.

Beijing has named the South China Sea one of its "core interests," meaning it could potentially go to war to protect it. Smaller Asian nations were already wary of China's growing military prowess, but the launch of its first carrier is yet another message about its increasing strength.

"We hope that China, as a major power, will contribute positively and responsively to maintain peace and stability in the region and in the world," Vietnam Foreign Ministry spokeswoman Nguyen Phuong Nga said last week in response to a question about China's new carrier.

China claims nearly all of the South China Sea, which the US has said it has a national interest in making sure freedom of navigation continues in an area home to vital shipping lanes.

Vietnam, the Philippines and several other Asian nations also stake claims to all or part of areas of the sea believed to be potentially rich in national resources. Both counties have looked to the US following recent blowups with China over their oil exploration activities. Beijing denies it has interfered, but Hanoi and Manila have accused the communist giant of overstepping its bounds.

Hanoi has reacted sharply, holding live-fire drills in the South China Sea and allowing rare protests to be held for more than two months. The tightly controlled communist government typically stamps out any demonstrations quickly, but on Sunday some 200 people again marched around Hanoi's central Hoan Kiem Lake chanting "Down with China!"

"From Vietnam's point of view, and from the point of view of maintaining a consistent and persistent claim to sovereignty, the protests by Vietnam are necessary and in its interests," said David Koh, a Vietnam expert at the Institute of Southeast Asian Studies in Singapore. "I do not think it is a matter of pulling back."

Analysts see China's carrier programme mainly as a prestige project with limited military capabilities, but one that could have major diplomatic implications for its neighbours.

"It will likely reinforce ongoing efforts by many regional countries to shore up their own capabilities," scholars Bonnie Glaser and Brittany Billingsley said in an analysis for the centre for Strategic and International Studies.

Last month, top Chinese Gen. Chen Bingde publicly scolded Adm. Mike Mullen, chair of the US Joint Chiefs of Staff, during his visit to Beijing, saying the US decision to hold joint maritime exercises with the Philippines and Vietnam was bad timing and could have been rescheduled, given the current rifts.

Mullen defended the exchanges, saying they were pre-planned.

"I consider this visit good timing. There is never bad timing," Lausman said of Saturday's carrier visit. "We are operating in international waters together as friends. There's never a bad time for friends to get together and meet."

Three US Navy ships paid a port call to the central Vietnamese city of Danang last month for joint exchanges, including search-and-rescue operations. The Vietnam War ended in 1975, but the former enemies have worked to strengthen military ties since relations were normalised in 1995.

The Philippines, a US ally, has also recently sparred with China, also alleging interference with its energy exploration efforts in the South China Sea. The US conducted naval exercises there in June, including live-fire drills.

The USS George Washington is essentially a floating city that can house some 5,000 sailors and pilots, as well as 70 aircraft, and is equipped with its own hospital. Based in Japan, it is one of the world's largest warships and can haul about 4 million pounds (1.8 million kilograms) of bombs.

Pilots blasted off from the flight deck during the weekend visit, soaring over the South China Sea as the Vietnamese and US Embassy visitors angled their cameras for souvenir photos of the powerful display.

"It took us a hundred years to get right here," Lausman said of the Navy's century of building aircraft carriers. "And we have 11 of these throughout the world right now, not just one."

By Margie Mason - The Associated Press - August 15, 2011