Farmland has also been endangered, with thousands of hectares off limits because of mines underneath.

"During the first mission, our task was mainly to remove mines along the border pass and roads where frontier defense soldiers usually patrolled," Fu recalled. Experts came all the way from Beijing to offer expertise and equipment such as metal detectors.

"Each time we completed de-mining, we always stomped and walked along the area before we turned it over to local governments," he said.

The first mission, between 1992 and 1994, removed mines in 102.8 sq km and closed off mined areas of 159.46 sq km to prevent injuries. Fu said, from then on, the number of human mine-related accidents fell, although livestock were often killed.

The second campaign, which the PLA said was the largest in world military history, was conducted between 1997 and 1999 on the border in two southwestern autonomous regions of Yunnan and Guangxi.

With experience and an unspecified increase in spending, better results were obtained, the local military area command said.

More than 500,000 landmines and 180,000 explosives were unearthed. At the Sino-Vietnam War's main battlefield, the smell of thousands of hectares of tea plants grown after 1999 replaced the previous choking smoke caused by exploded mines.

Mine removal has paved the way for prosperous border trade. China has been Vietnam's largest trade partner for more than two years, with trade hitting 16.6 billion U.S. dollars in the first 10 months of this year, surpassing the total 2007 figure, according to the Chinese government. Leaders of the two countries have set a target of 25 billion U.S. dollars by 2010, it said.

They also pledged to speed the creation of sub-regional economic areas, including a China-ASEAN (the Association of Southeast Asian Nations) free trade zone and trade corridors along the Mekong River, which originates in China, runs through Myanmar, Laos, Thailand, Cambodia and Vietnam and empties into the South China Sea.

"A peaceful border is part of any promising relationship between two armies and two countries and provides opportunities for increasing mutual respect and trust," said Jiang Yi, research fellow with the Chinese Academy of Social Sciences.

However, the danger of landmines has not been completely eliminated. It was estimated there were about 40 sq km of mined fields after two previous de-mining missions, with more than 500,000 mines and explosives remaining.